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THE 


Fogs  and  Fog  Signals 


-OF    THE — 


pacific  6fo$  of  the  United  jStateg. 


pubiis^d  for  tl?$  115%  of  8r;ip(T\a5t<?r$,  Ou/i}<?rs  ai}d  flQ^ts  interested 
ir;  tr;e  ^offlffl<?re<?  ar;d  jtfauigatior;  of  tl?<?  pacific;  (^oast. 


By  FERDINAND  LEE  CLARKE 

Corresponding  Member  California  Academy  of  Sciences. 


SAN  FRANCISCO: 

A.   I..  VALLEA.U,    PRINTER,  534  COMMERCIAL  STREET. 

lS38. 


COPYRIGHTED   BY 

FERDINAND  LEE  CLARKE- 
1889. 


BANCROFT  LIBRARY 
KENTFIELD  PAPERS 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

Microsoft  Corporation 


http://www.archive.org/details/fogsfogsignalsofOOclarrich 


THE 


Fogs  and  Fog  Signals 


— OF    THE — 


pacific  Coast  of  the  United  $Mz$. 


published  for  tl?<?  us<?  of  Shipmasters,  Outers  apd  p^epts  Interested 
ir;  tl?<?  ^om^er^  ar?d  ftavigatior;  of  tl?<?  pagfie  Qoast. 


By  FERDINAND  LEE  CLARKE, 

Corresponding  Member  California  Academy  of  Sciences. 


SAN  FRANCISCO: 

A.    L.  VALLEAU,  PRINTER,   534   COMMERCIAL  STREET. 


VK 


:  b 


Copyright  secured  according  to  law  by  Ferdinand  Lbe  Clarke, 
San  Francisco,  California,  November,  1888. 


3  4  5"  2  -^ 


THE 

Fogs  and  Fog  Signals 

OF  THE  PACIFIC  COAST. 


i^~  f  HE  Atlantic  and  Pacific  coasts,  the  lake  shores,  and  the  navigable  portion 
Ij  j  of  the  great  rivers  of  the  United  States  are  well  provided  with  lights,  fog  sig- 
sjj)  nals,  buoys, and  other  aids  to  navigation.  All  of  these  are  under  the  control 
of  the  Lighthouse  Board  of  the  United  States  and  are  grouped  in  sixteen  districts. 
According  to  the  official  report  of  the  board  for  1887,  there  were  on  June  30th  of 
that  year  2,034  "lighted"  and  4,464  "unlighted"  aids  to  navigation  in  position. 
Of  the  latter  there  were  217  fog  signals  operated  by  steam,  hot  air,  or  clock-work, 
44  whistling  buoys,  and  51  bell  buoys. 

In  the  Xllth  and  Xlllth  Districts,  011  the  Pacific  Coast  of  the  United  States— 
with  which  we  are  more  immediately  concerned,  and  to  which  the  substance  of 
this  pamphlet  will  be  more  particularly  confined — there  are  16  fog  signals,  12  of 
which  are  operated  by  steam,  or  hot  air,  the  others  by  clock  work,  and  12  whistling 
buoys.     These  are  all  first  class  instruments,   and  are  located  and  sounded  as 

follows : 

Xllth    DISTRICT. 

1.  Point  Conception,  12  inch  steam  whistle,  8  second  blast,  52  second  interval. 

2.  Ano  Nuevo  Island,  12  inch  steam  whistle,  10  second  blast,  55  second  interval. 

3.  Pigeon  Point,   12  inch  steam  whistle,    4   second   blast,    7    second    interval, 

and  4  second  blast,  45  second  interval,  alternately. 

4.  Point  Montara,  12  inch  steam  whistle,  5  second  blast,  25  second  interval. 

5.  Farallon,   first  class  steam  siren,  5  sec.  blast,  45  sec.  interval. 

6.  Point  Boneta,  first  class  steam  siren,  4  sec.  blast,  35  sec.  interval. 

7.  Fort  Point,  bell  struck  by  machinery  every  10  seconds. 

8.  L,ime  Point,  12  inch  steam  whistle,  10  sec.  blast,  30  sec.  interval. 

9.  Alcatraz,  bell  struck  by  machinery  5  blows  at  intervals  of  10  seconds,  followed 

by  an  interval  of  25  seconds. 

10.  Angel  Island,  bell  struck  by  machinery,  a  double  blow  every  15  seconds. 

11.  Yerba  Buena,  10-inch  steam  whistle,  4  second  blast,  16  second  interval.    If  the 

steam  whistle  is  disabled,  bell  will  be  struck  at  intervals  of  10  seconds 
until  whistle  is  ready  again. 

12.  East  Brother  Island,  12-inch  steam  whistle.    Alternate  blasts  of  8  and  4  seconds 

at  intervals  of  24  seconds.     At  the  beginning  of  fog,  or  if  steam  whistle  is 
disabled,  a  bell  will  be  struck  by  hand  at  intervals  of  about  15  seconds. 


13-  Mare  Island,  bell  struck  by  machinery  every  10  seconds. 

14.  Point  Reyes,  first  class  steam  siren  ;  5  second  blast,  70  second  interval. 

15.  Point  Arena,  1 2 -inch  steam  whistle  ;  5  second  blast,  25  second  interval. 

16.  Humboldt,  12-inch  steam  whistle  ;  alternate  blasts  of  4  and  8  seconds  ;   inter- 

vals 24  seconds. 

XHIth   DISTRICT. 

17.  Tillamook  Rock,  first-class  steam  siren  ;  5  second  blasts,  90  second  intervals. 

18.  Cape  Flattery,  12-inch  steam  whistle  ;  8  second  blast,  52  second  interval 

19.  Ediz  Hook,  bell  struck  by  machinery  every  15  seconds. 

20.  New  Duugeness,  12-iuch  steam  whistle;  6  second  blast,  12  second  interval  al- 

ternating with  3  second  blast,  39  second  interval. 

21.  Point  Wilson,  12-inch  steam  whistle;  8  second  blast,  52  second  interval. 

22.  Point-No-Point,  bell  struck  by  machinery  every  10  seconds. 

23.  West  Point  (Sandy  Point),  Daboll  trumpet ;  5  second  blast,  25  second  interval. 

24.  Point  Robinson,  12  inch  steam  whistle  ;  6  second  blast,  54  second  interval. 
The  signals  to  be  placed  at  other  points  will  be  :    Point  Sur,    steam  siren  ; 

Point  L,ouis  Obispo,  steam  siren ;  N.  W.  Seal  Rock,  steam  fog  whistle  (probably). 

The  distance  at  which  it  is  calculated  the  sound  from  the  signals  should  be 
heard  is  as  follows  :  12-inch  whistle,  5  miles;  10- inch  whistle,  5  miles;  steam 
siren,  5  miles  ;  bell,  from  1  to  3  miles. 

These  distances  are  purely  theoretical,  the  sound  of  any  signal  being  so  much 
affected  by  the  location,  atmosphere  and  other  causes,  as  to  render  the  question  of 
the  range  of  audibility  a  very-  complex  one.  As  a  rule  quite  as  much  depends 
upon  the  quality  of  the  tone  of  the  whistle  or  bell  as  on  anything  else. 

The  map  given  of  the  coast  line  shows  the  position  of  these  signals,  and  in 
addition  to  them  there  are  nearly  100  day  beacons  and  buoys,  and  fog  signals  are 
now  being  erected  at  Point  Sur  and  Point  L,ouis  .Obispo,  and  a  first-class  signal 
will  be  placed  on  N.  W.  Seal  Rock,  off  Crescent  City,  as  soon  as  the  lighthouse 
now  being  built  there  is  finished. 

Among  the  most  important  of  the  fog  signals,  the  "  whistling  "  buoys  rank 
first.  Those  on  this  coast  are  located  as  follows  :  off  Humboldt ;  off  Blunt' s  Reef 
near  Cape  Mendiciuo  ;  off  Fort  Bragg  Lauding  ;  outside  the  bar  of  San  Francisco  ; 
off  Santa  Cruz  ;  off  Point  Pinos  ;  off  Point  Sur  ;  off  Point  Pedros  Blancos  ;  off 
Point  Harford  ;  off  Point  Arguello  ;  off  Richardson's  Point,  south  side  of  west  end 
of  Santa  Barbara  Channel,  in  40  fathoms  of  water;   and  off  San  Diego. 

The  one  now  in  position  off  Point  Harford  will  be  moved  to  off  Point  Buchon, 
about  8  miles  north  of  Point  Harford,  as  vessels  from  San  Francisco  bound  to 
Port  Harford  change  their  course  at  Point  Sur  for  Point  Buchon,  which  is  a  very 
foggy  locality,  and  one  they  have  to  make  before  steering  for  their  port  of  destina- 
tion.    When  this  change  is  made,  a  bell  buoy  will  be  located  off  Point  Harford. 

A  whistling  buoy  will  also  be  put  in  position  off  Crescent  City,  and  one  has 
been  asked  for  to  be  placed  off  Point  Gorda,  14  miles  below  Mendocino. 

Owing  to  the  prevalence  of  fog  on  this  coast,  especially  in  the  months  of 
August  and  September,  the  importance  of  the  sound  signals  established  cannot 


be  over-estimated,  and  it  is  to  some  peculiarities  or  eccentricities  connected  with 
the  audibility  of  these  signals  that  attention  will  be  called  in  this  pamphlet,  and 
their  location  and  probable  origin  determined  as  far  as  possible  from  the  actual 
experience  of  navigators  on  this  coast,  as  well  as  from  results  obtained  from  ex- 
periments made  by  such  eminent  scientists  as  Professor  Tyudall  in  England,  and 
Professor  Henry  in  the  United  States,  as  well  as  by  naval  officers  of  both  coun- 
tries, on  the  audibility  of  sound  signals. 

To  present  these  peculiarities  intelligently,  the  conditions  affecting  the  for- 
mation of  fog  on  this  coast  will,  naturally,  be  first  discussed,  and  in  this  connec- 
tion the  matter  cannot  be  presented  in  a  clearer  manner  than  by  quoting  the  fol- 
lowing, which,  with  the  accompanying  diagram,  is  taken  from  a  paper  on  "The 
Temperature  of  the  Water  of  the  Golden  Gate, ' '  read  by  Professor  George  David- 
son, and  publisjied  in  Bulletin  No.  4,  California  Academy  of  Sciences,  1885: 

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At  the  tidal  station  of  the  United  States  Coast  and  Geodetic  Survey  at  Fort  Point  on  the  south 
shore  of  the  Golden  Gate,  and  at  Sausalito  on  the  north  shore,  where  it  was  subsequently  located,  the 
observer  notes  the  temperature  of  the  air  and  water  several  times  each  day.  A  tabulation  of  the  tempera- 
ture of  the  surface  water  and  of  the  air  has  been  made  for  the  seven-o'clock  morning  observations,  from  the 
daily  record  of  the  ten  years  extending  from  January,  1874,  to  December,  1883.  This  condensed  table  shows 
that  the  lowest  temperature  of  the  water  is  for  the  month  of  January,  50.49  degrees  Fahr.,  and  the 
highest  for  the  month  of  September,  59.68  degrees  Fahr,;  and  thus  the  average  range  is  only  nine  de- 
grees. The  lowest  monthly  temperature  observed  was  in  January,  1883,  when  it  reached  47.9  decrees, 
and  the  highest  in  August,  1880,  61. 1  degrees.  The  highest  range  in  January  was  53.9  degrees  in  1878, 
and    the  lowest  in  September  was  57.9  degrees  in  1874. 

The  temperature  of  the  air  follows  very  closely  that  of  the  water,  being  47.8  degrees  for  January, 
and  58.8  degrees  for  September  :  but  the  month  for  the  highest  temperature  was  June,  being  60.3  de- 
grees. The  tables,  however,  clearly  indicate  in  detail  the  great  uniformity  of  the  temperature  of  the 
water  off  this   part  of  the  coast,  and  of  the  air  within  fifteen  feet  of  the  surface  of  the  water. 

It  is  this  uniformity  of  temperature  of  the  sea  water  along  the  Pacific  Coast,  and  its  low  temper- 
ature, which  conspire  with  alternating  warm  and  comparatively  quiet  periods  and  the  northwest  winds 
of  summer  to  give  the  peculiar  foggy  conditions  which  prevail. 

The  graphical  platting  of  the  temperatures  of  the  air  and  water  in  the  Golden  Gate,  shown  above, 
suggests  the  intimate  relation  existing  between  the  periods  of  fog  and  the  periods  of  greatest  difference 
ln  temperature  of  air  and  water. 

When  the  monthly  mean  temperature  of  the  air  for  ten  years,  observed  at  8  A.  M.,  was   platted   on 


the  same  scale,  it  was  found  to  fall  below  the  temperature  of  the  water  from  April  to  September  inclusive, 
and  to  be  above  for  the  balance  of  the  year  ;  but  when  the  monthly  mean  of  three  daily  observations,  at 
4  A.  M.,  12  M.  and  8  P.  M.,  for  ten  years  was  platted  on  the  same  scale,  it  was  found  to  be  practically 
the  same  as  the  temperature  of  the  water  during  May,  June  and  September  ;  to  be  above  the  tempera- 
ture of  the  water  from  October  to  April  inclusive,  and  to  fall  below  the  temperature  of  the  water  only  in 
July  and  August.    July  and  August  are  the  seasons  of  almost  continuous  fogs. 

It  would  seem,  therefore,  that  whenever  the  temperature  of  the  air  falls  below  that  of  the  water, 
which  latter  is  very  uniform,  fogs  are  formed  ;  and  their  density  and  continuance  depend  upon  the  pre- 
ponderence  during  the  whole  twenty-four  hours  of  a  temperature  of  the  air  lower  than  that  of  the    water. 

Lieutenant  Maxfield,  U.  S.  A.,  in  charge  of  the  office  of  the  U.  S.  Signal 
Bureau  in  this  city,  gives  it  as  his  opinion  that  "The  amount  of  fog  on  this  coast 
during  the  summer  months  depends  in  a  great  measure  upon  the  strength  or 
steady  continuance  of  westerly  winds  during  the  season.  And  the  strength  of  such 
winds  is  in  proportion  to  the  rarefication  of  air  over  the  great  valleys  and  arid  areas 
west  of  the  Rocky  Mountains." 

In  accordance  with  the  above,  it  follows  that  if  the  early  spring  and  summer 
months  are  dry  and  warm  back  from  the  coast  line,  there  will  be  a  greater 
amount  of  fog,  or  the  fog  will  occur  earlier  in  the  season,  than  when  we  nave 
throughout  California  a  "backward"  spring. 

In  confirmation  with  this  is  the  opinion  expressed  to  the  writer  by  more  than 
one  close  observer,  that  a  wet  spring  retards  the  arrival  of  fogs  on  this  coast — 
seems  to  push  them  along  to  later  in  the  season. 

The  cause  of  fogs  having  been  thus  briefly  set  forth,  their  season  and  rel- 
ative amount  come  next  under  consideration.  In  collecting  data  on  this  subject 
the  writer  has  examined  the  records  of  the  Lighthouse  Department  in  this  city, 
to  which,  through  the  courtesy  of  Commander  Nicholl  Ludlow,  U.  S.  N.,  the  In- 
spector in  charge  of  this  district,  he  has  been  given  free  access,  and  from  them  has 
compiled  the  following  chart,  which  gives  the  number  of  hours  in  each  month 
from  July,  1876,  to  July,  1888, — twelve  years — during  which  the  fog  signals  at 
the  stations  named  were  sounded  : 

In  this  as  well  as  the  third  diagram,  each  horizontal  line  is  a  zero  point  for 
the  station  whose  name  is  immediately  above  and  bracketed  to  it,  and  the  stations 
are  arranged  approximately  with  regard  to  their  geographical  position,  as  will  be 
seen  by  reference  to  the  map.  As  has  been  intimated,  August  and  September  are 
the  two  months  when  there  is  the  most  fog  at  all  the  stations,  the  quantity  reach- 
ing the  maximum  in  September  at  all  stations  south  of  Farallou,  and  in  August  at 
the  other  stations  until  we.  reach  Humboldt,  when  it  again  culminates  in  Sep- 
tember. 

An  examination  of  the  diagrams  show  that  the  period  of  fog  coincides  with 
the  time  when  the  air  temperature  is  below  that  of  the  water,  and  that  at  all  the 
coast  stations  except  Conception  (which,  being  over  two  hundred  miles  in  an  air 
line  south  of  the  next  station, — Point  Ano  Nuevo — may  be  considered  as  out  of 
the  conditions  that  prevail  at  the  other  stations,  and  at  Point  Arena),  the  minimum 
of  fog  is  found  in  April.  In  this  connection  and  to  assist  the  reader  in  under- 
standing the  values  expressed  by  the  profile  lines  in  the  first  chart,  the  follow- 
ing figures  are  given  of  maximum  and  minimum  fog,  at  the  principal  stations  in 


July.     Aug.      Sept.      Oct.      Nov.      Dec.      Jan.      Feb.      Mch.     April.     May.    Ji 


Humboldt 


1 

~~~" 

-    ... 

COMPARATIVE   DIAGRAM   OF   FOG.      NO.  I. 


the  Xllth  district  during  the  period  in  which  the  signals  have  been  in  operation 
up  to  July  ist,  1888  : 

Station.  Period  in  Operation. 

Point  Conception 11  years,  10  months. 

Ano  Nuevo 11      "       10       " 

Pigeon  Point n      "       II        " 

Montara 11      "       n        " 

Farallon    7     "       10 

Bonita 12     "       00       " 

Lime  Point 4     "       10       " 

Point  Reyes II      "       10       " 

Point  Arena 11      "       11        " 

Humboldt II      "       10       " 

Combining  the  profiles  given  above  by  adding  together  the  totals  of  each 
mouth  we  obtain  a  second  profile,  illustrating  the  relative  amount  of  fog  on  the 
coast  line  of  this  light-house  district   for   twelve   years.     (The  reports  from    the 


Max. 

Hours 

Min. 

Hours 

Septemlx:r, 

488. 

January 

100. 

" 

1671. 

April, 

408. 

<i 

1784. 

" 

385. 

" 

1636. 

" 

412. 

August, 

I485. 

" 

3*4- 

': 

2768. 

" 

800. 

September, 

626. 

" 

70. 

August, 

3012. 

" 

760. 

" 

20l8. 

January, 

324- 

September, 

2502. 

April, 

263. 

1 1 r~ 1 1 j 1 T J T 

J&\W\ — 


SUMMARY   OF   FOG    FOR   TWELVE   YEARS.       NO.  2. 

light-houses  and  signal  stations  north  of  Humboldt,  i.  e.,  in  the  XIHth  District 
have  not  been  examined  in  detail,  but  it  is  known  that  the  quantity  and  duration 
of  fog  increases  as  we  go  northward,  until  it  prevails  for  the  most  of  the  year  on 
the  Alaskan  Coast.) 

In  the  following  diagram  and  table  the  amount  and  time  of  fog  at   what  may 
be  termed  the  "  Bay,"  or  "  inside  "  fog  signal  stations,  is  given  : 

Station.                                       Period  in  Operation.                  Max.               Hours.  Min.  Hours. 

Angel  Island 1  years,  9  months.  Semptember,     64.00.  April,  5.00. 

Alcatraz 6     "                                     '*               634.0b.         "  65.00. 

Verba  Buena .6     "  January,           400.00.          "  1.00. 

East  Brother 6     "                                  "                  406.00.         "  1.00. 

Mare  Island 6     "                                  "                  518.00.          "  2.00. 


Mare  Island.. 


Yerba  Buena.. 


Angel  Island. 


<Wtt»mta>| 


il* 


tA 


Alcatraz. 


Jul.    Au.    Sep.  Oc.  No.    De.    Ja.    Fe.    Mh.  Apl.  M.  Jun. 
COMPARATIVE    DIAGRAM    OF    FOG.       NO.   3. 

It  will  be  seen  that  the  season  of  maximum  and  minimum  fog  gradually 
changes  as  we  leave  the  coast  line  until,  at  Mare  Island,  the  months  of  December 
and  January  have  the  most  fog.  The  cause  of  this  change  is  not  difficult  to  ex- 
plain if  it  is  borne  in  mind  that  fog  exists  where  the  air  is  colder  than  the  body  of 
water  on  which  it  rests.  In  the  winter  months — that  is,  from  December  to  Feb- 
ruary and  March — the  waters  of  both  the  Sacramento  and  San  Joaquin  rivers  are 
at  their  lowest  and  thoroughly  warmed.  After  entering  Suisun  Bay,  they  spread 
out  over  a  large  area,  and  being  shallow  are  still  more  heated,  so  that  they  are 
several  degrees  warmer  than  the  air  moving  in  from  the  sea.  This  cool  air  con- 
denses a  large  percentage  of  the  moisture  which  has  been  evaporated  from  the 
rivers,  and  it  appears  as  fog.  But  later  in  the  season  the  snows  in  the  Sierras 
begin  to  melt,  and  the  resultant  cold  waters  find  their  way  into  the  two  rivers 
and  from  them  are  poured  into  the  bay,  chilling  its  waters  to  below  the  tempera- 
ture of  the  air  above,  and  there  are  no  fogs. 

In  the  following  diagram  the  relative  amount  of  fog  prevailing  along  this 
coast,  from  Point  Concepciou  to  Humboldt,  during  each  month  of  the  year,  is 
given.  As  it  is  only  at  the  stations  designated  that  observations  have  been  made, 
the  amount  of  fog  prevailing  between  them  is  only  conjectural,  but  it  is  fair  to 
assume  that  at  the  mouths  of  the  few  important  streams  that  empty  into  the  sea 
on  this  line  there  is  formed  more  fog  than  elsewhere.  Hence  the  outline  of  the 
fog  diagram  would  be  elevated  somewhat  at  such  points. 

In  studying  any  attempt  at  the  graphic  delineation  of  fog,  it  must  be  borne 
in  mind  that  the  mass  of  vapor  is  not  homcegeneous  as  regards  quantity,  nor  con- 
stant as  regards  location.  While  it  is  probable  that  there  never  is  a  day  when 
fog  does  not  prevail  somewhere  on  this  coast  line,    yet  there  are  times  when  it 


IO 


fe=« 


^^ 


,  i 


Point  Arena 


Point  Reyes....  | 

Point  Boneta.. 

Farallon 

Lime  Point 


|  ...Afio  Nuevo.      Pt.  Concepcion.  | 
I  ...Pigeon  Point. 
Point  fiontanu 


does  uot  seriously  interfere  with  free  navigation.  And  when  it  does  so  prevail 
it  varies  greatly  in  density  and  character.  From  the  evidence  of  those  who  have 
made  the  formation  and  appearance  of  fog  their  study,  it  appears  that — on  this 
coast,  at  least,  and  especially  off  the  entrance  to  San  Francisco  harbor — it  occurs 
in  strata  or  layers,  the  thicker  fog  being  lower  down,  the  thinner  above.  Clear 
spaces  often  occur  in  the  bank  of  fog  ;  and,  in  short,  the  density,  vertical  and  hor- 
izontal thickness,  and  duration  of  fog  are  all  three  variable  quantities,  as  might 
be  expected  from  the  varying  action  of  the  causes  producing  the  phenomenon. 
Vapor  exists  in  air  much  as  air  does  in  water ;  that  is,  as  a  separate  element. 
However  minute  we  may  conceive  the  final  atom  of  air  or  water  to  be  (and  the 
sub-division  may  be  carried  to  that  extent  that  the  ultimate  particle  is  of  incon- 
ceivable smallness),  there  still  remain  atoms  or  vesicles  the  aggregation  of  which 
make  up  the  volume  of  both  elements.     In  nature  the  two  cannot  be  conceived  of 


II 

as  existing  separately,  though  the  proportion  they  bear  to  each  other  is  constantly 
varying.  In  ice  the  aqueous  element  holds  a  minimum  quantity  of  air.  Water 
is  made  up  of  more  equal  proportions  of  each,  while  in  "fog,"  or  visible  vapor, 
air  prevails  to  a  greater  extent,  and  a  normally  clear  atmosphere  contains  mois- 
ture in  a  still  less  degree. 

The  amount  of  aqueous  vapor  actually  existing  in  a  body  of  air  is  not  necessa- 
rily fully  indicated  by  the  quantity  visible.  That  is  to  say,  a  body  of  air  may  con- 
tain a  certain  percentage  of  moisture — in  fact,  may  be  filled  almost  to  the  point  of 
saturation  with  aqueous  vapor- — which  may  not  be  apparent  to  the  eye  simply  be- 
cause it  exists  in  too  fine  a  state  of  sub-division  to  interfere  with  the  transmission 
of  light.  But  if  a  current  of  cold  air  enter  the  area,  the  vapor  in  its  track  is  chilled 
and  condensed,  at  first  into  minute  vesicles,  and  has  to  give  up  a  certain  percent- 
age of  its  moisture  which  is  thus  made  visible.  This  is  often  finely  illustrated  in 
elevated  and  broken  areas  of  land  where  the  topography  is  favorable  to  the  forma- 
tion of  erratic  currents  of  air.  There  vapor  or  fog  will  be  seen  to  form  on  the  crest 
or  side  of  peaks,  and,  to  the  eye,  will  seem  to  move  in  wreaths  and  folds  about  the 
hollows  and  elevations,  sometimes  condensing  into  snowy  masses  that  apparently 
pour  over  crags  and  precipices  only  to  be  dissolved  in  the  lower  depths,  or  to  float 
and  vanish  in  the  surrounding  warmer  air.  So,  too,  the  mariner  sailing  over  the 
ocean,  beneath  a  summer  sky  and  in  a  clear  atmosphere,  not  unfrequently  sees 
forming  on  the  horizon  a  mass  of  vapor  which,  with  the  sudden  chill  he  feels  as 
his  vessel  enters  the  misty  meteor,  warns  him  of  a  change  in  the  weather,  and,  in 
certain  latitudes,  of  the  presence  of  icebergs  in  his  vicinity. 

As  regards  the  movement  of  areas  of  fog,  it  may  be  said  that  this  is  more  ap- 
parent than  real.  Generally  speaking,  it  is  not  the  mass  of  vapor  seen  at  one 
point  that  moves  toward  or  from  the  observer,  any  more  than  it  is  the  mass  of 
water  forming  an  advancing  wave  that  moves  forward  as  the  undulation  pro- 
gresses. But,  unlike  the  watery  wave  which  owes  its  onward  progress  to  the  trans- 
mission from  one  point  to  another  in  the  liquid  mass  of  the  force  that  generated 
the  movement,  the  apparent  onward  movement  of  a  mass  of  fog  is  due,  for  the 
most  part,  to  the  progressive  movement  of  the  volume  of  cold  air  making  the 
moisture  visible.  Of  course  a  strong  current  of  air  will  carry  with  it  an  apprecia- 
ble quantity  of  the  visible  moisture  which  it  has  condensed,  as  rain  will  be  trans- 
mitted beyond  the  area  of  its  formation.  But  such  transference  is  purely  mechan- 
ical, and  has  little  to  do  with  the  formation  of  either  the  fog  or  rain. 

Having  thus  briefly  touched  upon  the  origin  of  fogs  upon  this  coast,  their 
prevalence,  and  their  nature,  it  will  be  in  order  to  treat  upon  the  effect  these  masses 
of  vapor  have  upon  sound. 

In  regard  to  the  effect  produced  upon  sound  by  fog,  opinions  seem  to  differ 
widely.  Lieutenant  Commander  Chadwick,  U.  S.  N.,  one  of  the  lighthouse  in- 
spectors, who  had  charge  of  the  lighthouse  steamer  when  observations  on  this 
subject  were  being  made  on  the  Atlantic  coast,  and  who  had  made  the  whole  ques- 
tion the  subject  of  careful  study,  says : 

"  Fog,  to  my  mind  and  as  far  as  my  experience  goes,  is  not  a  factor  of  any  consequence  whatever 
in  the  question  of  sound.  Signals  may  be  heard  at  great  distances  through  the  densest  fogs,  which  may 
be  totally  inaudible  in  the  same  directions  and  at  the  same  distances  in   the  clearest  atmosphere.     It  is. 


12 

not  meant  by  this  last  statement  that  the  fog  may  assist  the  sound,  as  at  another  time  the  signal  may  l>e 
absolutely  inaudible  in  a  fog  of  like  density,  where  it  had  before  been  clearly  heard.  That  fog  has  no 
great  effect  can  be  easily  understood  when  it  is  known,  as  it  certainly  is  known  by  observers,  that  even 
snow  does  not  deaden  sound,  there  being  no  condition  of  the  atmosphere  so  favorable  for  the  far-reaching 
of  sound  signals  as  that  of  a  heavy  northeast  snowstorm,  due  supposedly  to  the  homogenity  produced  by 
the  falling  snow." 

At  the  same  time  there  are  not  a  few  practical  shipmasters  on  this  coast  who 
have  told  the  writer  that  they  have  repeatedly  noticed  the  echo  of  sound  from  a  dense 
fog  bank,  and  of  irregularities  of  sound  produced,  as  they  believe,  by  the  varying 
thickness  of  the  fog.  Professor  George  Davidson  of  the  Coast  and  Geodetic  Sur- 
vey, speaking  on  this  subject,  said  that  he  was  of  the  opinion  that  a  wall  of  fog 
will  reflect  sound,  and  open  patches  of  fog  confuse  sound  and  render  its  source 
uncertain.  In  the  Arctic  Ocean  the  writer  has  noticed  the  echo  of  sound  spoken 
of  at  times  when  fogs  prevailed  under  such  circumstances  as  to  make  it  absolutely 
certain  that  the  sound  was  thrown  back  from  the  dense,  dirty  gray  wall  of  vapor 
close  at  hand. 

Sound  waves  are  sensibly  deflected  from  their  course  by  media  that  do  not 
alter  the  path  of  light  waves  to  the  same  extent,  rays  of  light  being  able  to  pass 
practically  straight  through  stratas  of  unequally  heated  air,  through  fog  and  mist 
or  snow,  while  sound  waves  are  bent  up  or  down,  or  to  either  side, — nay,  some- 
times totally  extinguished, — in  encountering  the  same  obstructions.  When  the 
navigator  sees  a  luminous  point,  he  may  safely  conclude  that  the  source  from 
which  it  emanates  is  in  the  direction  from  which  the  rays  seem  to  proceed.  But  in 
the  case  of  sound  proceeding  from  an  invisible  point,  he  cannot  be  sure  that  it 
originates  in  the  direction  from  which  it  is  apparently  heard.  And  not  only  this, 
but  it  is  sometimes  impossible  to  hear  sound  signals  when  they  should  be  heard, 
or.  the  tones  when  heard  are  often  confused  and  misunderstood,  and  then  they  help 
to  precipitate  catastrophes  they  are  intended  to  avert.  These  facts  have  been 
proven  by  a  series  of  experiments  on  the  audibility  of  sound  signals,  made  by  such 
eminent  scientists  as  Prof.  Tyndall,  in  England,  and  Prof.  Henry,  in  the  United 
States,  as  well  as  by  naval  officers  of  both  countries.  These  experiments  were 
referred  to  at  length  in  a  paper  read  before  the  Philosophical  Society  of  Washing- 
ton, in  1881,  by  Mr.  Arnold  B.  Johnson,  Chief  Clerk  of  the  Lighthouse  Board, 
and  the  conclusion  is  arrived  at  that  the  popular  notion  that  "sound  is  always 
heard  in  all  drections  from  its  source  according  to  its  intensity  or  force,"  is  erron- 
eous, and  "brings  practical  men,  even  shipmasters,  to  grief." 

To  support  this  statement,  instances  are  cited  showing  that  when  fog  signals 
were  in  full  blast,  they  would  not  be  heard  with  the  intensity,  nor  at  the  places 
expected  ;  would  be  heard  faintly  when  they  ought  to  be  heard  loudly,  and  the 
reverse  ;  could  not  be  heard  at  all  at  times  when  close  by,  but  would  be  heard  dis- 
tinctly further  away  ;  and  all  these  changes  would  occur  within  reasonable  ear- 
shot of  the  source  of  sound.  In  one  case  a  steamer  grounded  in  a  dead  calm  and 
dense  fog  "  about  one-eighth' of  a  mile  from  and  behind  the  steam  siren,"  because, 
though  the  siren  was  in  full  blast,  it  was  not  heard  by  those  on  the  vessel.  In 
another  instance  those  on  board  a  steamer,  sent  out  for  the  special  purpose  of  test- 
ing the  audibility  of  sound  signals,  when  between  two  and  one-half  and  three  and 
one-half  miles  from  a  steam  siren,  heard  nothing  but   "a  faint  murmur,"   at  the 


13 

most,  though  there  seemed  to  be  no  reason  why  the  signal  should  not  have  been 
heard  for  at  least  twelve  miles. 

General  Duane,  U.  S.  A.,  in  a  report  made  in  1874  on  this  subject  to  the 
Lighthouse  Board,  says  : 

The  signal  is  often  heard  at  a  great  distance  in  one  direction,  while  in  another  it  will  be  scarcely 
audible  at  the  distance  of  a  mile.  This  is  not  the  effect  of  wind,  as  the  signal  is  frequently  heard  much 
farther  against  the  wind  than  with  it,  and  cites  as  an  example  the  steam  whistle  at  Cape  Elizabeth,  nine 
miles  distant  from  Portland,  Maine,  which  "can  always  be  distinctly  heard  with  the  wind  blowing  a  gale 
directly  towards  the  whistle." 

The  experience  of  many  of  our  pilots  on  this  coast,  as  well  as  the  evidence  of 
other  experienced  navigators,  goes  to  prove  that  certain  conditions  of  fog  are  favor- 
able to  the  production  of  echoes. 

Mr.  T.  P.  H.  Whitelaw,  who  for  many  years  has  had  occasion  to  note  the 
audibility  of  sound  signals  on  this  coast  while  affording  relief  to  wrecked  vessels 
and  recovering  materials  from  such,  says  : 

"  Clear  spaces  in  fog  banks  interrupt  or  alter  the  course  of  the  sounds  of  signals.  When  sound  strikes 
the  thick  strata  it  is  deflected  upward — sent  overhead — and  so  lost  ;  and  when  it  passes  into  lighter 
strata  or  open  spaces  it  is  heard  again." 

As  an  illustration  of  this  phenomenon  Mr.  Whitelaw  drew  the  following  dia- 
grams and  explained  them  as  follows : 


"  In  approaching  Point  Boneta,  and  when  about  six  miles  distant,  I  have  met  a  wall  of  fog  (A)  and 
could  hear  the  siren  on  the  Point  plainly.  Passing  through  this  there  has  occurred  a  clear  space  (B)  in 
which  the  siren  was  not  heard.  The  fog  seemed  to  arch  overhead,  touching  the  sea  again  at  (C)  about 
three  miles  from  the  Point.  Here  the  siren  was  heard  again,  and  as  soon  as  we  passed  into  the  open 
space  (D)  it  was  heard  but  faintly,  and  wholly  lost  when  within  one  and  a  half  miles  of  the  Point. 


"Again  ;  in  approaching  Point  Boneta,  the  sound  of  the  siren  has  been  heard  when  in  the  position 


14 


shown  in  the  second  diagram,  and  in  the  direction  of  its  source,  i.e.,  at  A.  But  when  the  vessel  had 
moved  to  a  position  '  2,'  the  siren  was  heard  as  coming  from  '  B, '  and  when  the  vessel  was  at  '3  '  the 
sound  was  then,  apparently,  from  '  C  ' 

In  the  sketch,  page  15,  of  the  entrance  to  the  Golden  Gate,  there  is  indicated  the 
Point  Bonita  light  and  signal  station,  at  which  is  located  a  siren  at  124  feet  eleva- 
tion above  sea  level.  On  the  same  shore  is  the  projecting  point,  Point  Diablo, 
and  further  in  is  Lime  Point,  on  which  is  located  a  twelve-inch  steam  whistle  30 
feet  above  sea  level.  Both  signals  should  be  heard  well  out  to  sea,  the  siren  espec- 
ially, whose  tones  should  be  heard  at  Farallon  station,  where  is  located  another  of 
the  noisy  sisterhood. 


Note. — The  accompanying  top- 
ographical drawing  of  Point  Bon- 
eta,  showing  the  location  of  the 
light-house  and  fog  signal,  has 
been  furnished  by  Mr.  Louil  A. 
Sengteller,  U.  S.  Coast  and  Geo- 
detic Survey,  from  the  survey  of 
the  locality  made  by  him  in  1881. 

The  light  is  displayed  from  a 
tower  on  the  west  point,  and  the 
fog  signal  is  located  on  the  narrow 
platform  near  the  south  end  of  the 
bluff,  the  mouth  of  the  siren  being 
directed  seaward. 


Point  Boneta  Light  House. 


Wharf. 


<£•  ''Iwlaa    Fog  Siren. 


It  is  the  experience  of  pilots  and  navigators  that  the  fog  signals  mentioned 
are  not  always  heard  on  this  coast  when  they  apparently  should  be,  and  some- 
times the  keeper  of  one  or  the  other  has  been  reported  as  not  having  his  signal  in 
operation,  when  investigation  has  proved  that  it  was  being  sounded  regularly 
when  thought  to  be  silent.  There  occur,  too,  here  "areas  of  inaudibility,"  and  al- 
though it  cannot  be  said  that  such  areas  are  alwa>-s  constant  as  regards  time,  or 
well  defined  as  regards  position,  yet  there  are  a  few  localities  where  they  may  be 
said  to  always  exist. 

On  the  south  shore,  coming  from  the  southward,  Point  Lobos  and  the  Seal 
Rocks  are  first  passed,  and  then  Mile  Rock.  Beyond  this  the  shore  sweeps  in  a 
tolerably  uniform  curve  towards  the  north,  terminating  in  Fort  Point,  almost  due 
south  from  Lime  Point,  and  one  mile  distant  from  it. 

The  land  on  the  north  shore  is  high,  the  240-foot  level  line — indicated  on  the 
map — following  closely  the  shore  line.  On  the  south  shore  the  sand  hills  are 
lower,  but  still  the  200-foot  level  is  found  generally  but  a  little  way  back  from  the 
beach. 

This  level  of  200  feet  is  selected  in  this  case  as  being  high  above  the  different 
signal  stations  near  it,  and  practically  extending  continuously  along  both  shores 
from  Point  Boneta  to  Lime  Point  on  the  north,  and  Point  Lobos  to  Fort  Point  on 
the  south.     What   effect   upon   sound  this  conformation  of  the  land  has  is    a 


15 

subject  of  great  importance  to  all  navigators  seeking  to  enter  the  Golden   Gate  in 
time  of  fog. 

For  example,  it  is  a  common  experience  of  navigators  entering  this  harbor 
and  keeping  along  the  north  shore,  to  lose  the  sound  of  the  whistle  on  L,ime  Point 
when  they  are  nearing  Point  Diablo,  though  after  they  pass  Point  Boneta  it  is 
generally  heard  distinctly  up  to  the  point  mentioned.  Another  example  occurs 
at  Point  Reyes  station.  The  steam  whistle  located  there  is  not  heard,  as  a  rule, 
at  all  north  of  the  station.  There  is  a  long  stretch  of  sandy  shore  there,  and  ves- 
sels have  often  found  themselves  dangerously  close  to  the  land  when  the  fog  lifted 
because  the  fog  whistle,  only  a  short  distance  south  of  them,  had  not  been  heard. 


A 


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turn 


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V 


\ 


ENTRANCE  TO  GOLDEN  GATE. 

There  have  also  been  noticed  at  various  points  on  the  coast  ' '  aberrations  of 
audibility  ' '  of  fog  signals,  caused  by  the  interference  of  waves  of  sound  with  each 
other,  or  the  formation  of  echoes.  Both  of  these  phenomena  exist  at  the  entrance 
to  the  Gate,  and  their  presence  may  perhaps  be  explained  by  reference  to  the  lines 
drawn  upon  the  chart  of  the  entrance  given  above. 

It  has  already  baen  said  that  the  land  upon  both  shores  of  the  entrance  to  the 


i6 
t 

Gate  is  substantially  higher  than  the  location  of  the  siren  at  Point  Boneta   or  the 

steam  whistle  at  Lime  Point.     If  a  line  be  drawn  from  Lime   Point  station — say 

at  ioo  feet  elevation  above  the  sea — so  as  to  touch  the  shore  between  Lime   Point 

and  Point  Diablo,  it  will  be  seen  that  it  will  form  the  arc  of  a  circle  whose  radius 

is  about  3,000  feet.     Another  line  drawn  from   Point  Diablo  to   Point    Boneta, 

touching  the  shore  line  at  an  elevation  of  200  feet,  will  form   the  arc  of  a  second 

circle  whose  radius  is  about  the  same  as  that  of  the  first  one.     A  third  line,   from 

Fort  Point  to  a  point  on  the  south  shore  opposite  Mile  Rock,  will  form  the   arc  of 

a  third  and  larger  circle  whose  elevation  above  the  sea  at  all  points  is  higher  than 

the  signal  at  Point  Boneta  and  Lime  Point.     Thus  there  is  found  behind  each  of 

the  two  fog  signals  on  the  north  shore  a  huge  reflector,  as  it  may  be  called,  which 

diverts  the  sound  waves  from  Point  Boneta  and  Lime  Point,  and  sends  them  across 

the  waters  toward  the  third  reflector  on  the  south  shore,   which  in  turn  reflects 

them  in  varying  angles,  some  of  which  are  illustrated  in  the  sketch. 

Thus  a  wave  of  sound  from  Boneta,  touching  the  circle  at  a  point  close  to  its 
source,  would  be  deflected  several  times  on  the  curved  surface,  finally  leaving  the 
north  shore  near  Point  Diablo,  and  crossing  the  water  would  be  sent  out  to  sea 
near  the  point  marked  a.  Another  wave  from  the  same  source,  however,  moving 
straight  across  from  its  initial  point  to  near  the  opposite  point  of  the  circular  arc, 
would  be  sent  from  there  out  to  sea  on  the  line  b.  So,  too,  a  wave  of  sound  c 
from  Boneta,  moving  straight  across  the  water  to  a  point  near  Fort  Point,  would 
be  thrown  back  to  near  line  b. 

A  fourth  wave,  Amoving  across  to  the  south  shore  near  Mile  Rock,  would  be 
thrown  back  into  the  harbor.  The  line  e,  after  being  deflected  on  the  arc  of  the 
large  circle,  would  cross  to  the  Lime  Point  arc,  and  from  there  into  the  harbor, 
crossing  d. 

So  with  reference  to  sound  from  the  Lime  Point  whistle.  A  sound  wave  f 
from  this  source  crossing  the  Gate  and  impigning  on  the  south-shore  arc,  would 
travel  around  it  and  emerge  on  the  line  /',  about  in  mid-channel.  A  second  wave, 
g,  moving  across  to  the  high  shore  in  from  Mile  Rock,  would  be  thrown  across  to 
the  Boneta  arc,  thence  back  to  the  south  shore,  and  finally  out  into  the  Boneta 
channel  on  the  line  g. 

These  illustrations  of  the  theoretical  track  of  some  of  the  sound  waves  set  in 
motion  by  the  two  fog  signals  mentioned  are  given  to  show  how  the  peculiar  con- 
formation of  the  land  on  both  sides  of  the  entrance  to  the  Golden  Gate  will  nec- 
essarily confuse  the  notes  of  the  signals,  and  at  some  points  render  them  inaudible. 

One  important  fact  is  that  the  greater  part  of  the  volume  of  reflected  sound  from 
both  signals  finds  its  way  to  sea  more  on  the  south  side  of  the  main  channel  than 
on  the  north.  Thus  vessels  approaching  this  point  from  the  south  are  more  apt 
to  hear  the  signals  than  when  coming  down  from  the  north.  At  the  same  time,  a 
navigator  after  passing  Mile  Rock  (which,  it  may  be  remarked,  should  be  removed), 
if  he  is  well  in  to  the  south  shore,  and  approximately  half  way  between  Mile  Rock 
and  Fort  Point  would  be  likely  to  hear  the  Boneta  siren  so  plainly  as  to  mislead 
him  in  regard  to  his  whereabouts  ;  or,  one  not  familiar  with  the  tones  of  the  two 


i7 

signals  might,  hearing  their  reflected  sound's,   imagine  them  to  be  placed  on  the 
south  shore,  where  it  would  not  be  safe  to  venture  far. 

The  lines  traced  on  the  chart  given  on  page  15.  are,  approximately,  tho.se  bound- 
ing the  areas  within  which  the  volume  of  sounds  reflected  from  the  shores  on 
either  side  of  the  entrance  to  the  Golden  Gate  would  be  heard.  Thus;  between 
the  points  a  and  b,  all  the  sounds  from  the  Boneta  signal  reflected  from  the  high 
land  between  that  point  and  Point  Diablo  would  be  heard,  while,  with  reference 
to  the  sound  from  the  Lime  Point  signal,  its  waves,  reflected  from  the  south  shore, 
would  be  heard  between/  and  g.  Owing  to  the  irregular  contour  of  the  hills 
behind  all  the  signals,  these  waves  of  sound  would  not  follow  invariably  the  theo- 
retical paths  clue  to  their  reflection  from  a  mathematically  correct  concave  surface, 
but,  upon  the  whole,  their  course  would  fall  within  the  lines  referred  to. 

There  are  several  points  where  it  is  probable  areas  of  inaudibility  are  pro- 
duced by  the  interference  of  the  waves  of  sound  from  the  two  signals.  One  such 
area  might  be  expected  to  exist  a  short  distance — from  a  half  to  three-quarters  of 
a  mile — west  of  south  from  Point  Diablo,  as  in  that  vicinity  the  direct  and  reflect- 
ed waves  from  Point  Boneta  meet  the  direct  wave  from  Lime  Point.  About  a 
mile  west  of  Point  Diablo  the  navigator  may  lose  the  sound  of  the  whistle  on  Lime 
Point,  as  he  is  then  out  of  range  of  its  direct  waves.  Again;  in  approaching 
Point  Diablo — going  out — the  sound  of  the  Boneta  siren  would  be,  in  a  great 
measure,  cut  off  by  the  point,  so  that  the  navigator  might  have  difficulty  in  pick- 
ing it  up. 

It  is  well  known  that  sound  waves  crossing  or  meeting  each  other  produce, 
when  the  two  are  in  harmony  with  each  other,  a  new  note,  and  it  is  the  ' '  concord  ' ' 
of  sounds  that  produce  musical  notes.  But  when  the  >l  pitch  "  of  two  sound-pro- 
ducing instruments,  be  they  organ  pipes,  steam  whistles,  bells  or  what-not,  are  not  in 
harmony  with  each  other,  the  result  of  their  sound  waves  meeting  each  other  is 
to  produce  a  discordant  "noise,"  which  is  weaker,  always,  than  either  of  the  orig- 
inal tones.  Hence  it  follows  that  Jwo  sound  signals  located  within  hearing  of 
each  other,  such  as  those  on  Boneta  and  Lime  Point,  might  with  advantage  be 
regulated  in  tone  so  that  their  combined  volume  would  produce  an  intermediate 
and  harmonic  note. 

In  some  localities  the  shape  of  the  land  in  the  vicinity  of  fog  signals  cuts  off 
their  sound  from  some  quarters.  On  the  Farallon,  for  instance,  Captain  Ludlow 
says  that  when  making  the  anchorage  from  the  east — inshore — side  of  the  rock  in 
foggy  weather  he  has  listened  in  vain  for  the  sound  of  the  siren,  nor  did  he  hear 
it  until  he  had  landed  and  climbed  the  rock  so  that  he  could  see  it  in  full  blast  on 
the  other  side. 

There  exist  in  the  immediate  neighborhood  of  the  Farallon  one  or  more  of 
those  mysterious  "areas  of  inaudibility,"  within  which  the  fog  siren  is  not  heard, 
though,  as  was  reported  by  the  captain  of  a  vessel  during  the  present  year,  the 
navigator  is  near  enough  to  hear  the  breakers  on  the  rock  very  distinctly.  It  may 
be  said  that  the  trumpet  of  the  siren  is  so  directed  as  to  throw  the  volume  of  sound 
in  the  direction  where  it  is  needed  for  vessels  coming  into  this  port,  though  those 
bound  out  do  not  derive  much,  if  any,  benefit  from  it, 


Note — The  cut  gives  the 

contour  of  the  South  Far- 

allon,  with  contour  lines  for 

every  twenty  feet  elevation. 

The  regular  landing  place 

is  on  the  north  side  where 

there    is  a   derrick.      The 

dotted   lines   indicate    foot 

paths  to  different  points  on 

the  island,  which  is  about  a 

mile  in  length  from  east  to 

west.      The  Middle  Faral- 

lon  lies  N.  W.   by  W.  2% 

miles  distant  from  the  light 

house  on  the  highest  point 

of   South   Farallon.      The 


north  islet  of  the  North 
Farallon  is  North,  640  West, 
six  and  three-fifths  miles 
from  the  lights.  Noonday 
Rock  lies  W.  by  N.  3  miles 
distance  from  North  Far- 
allon. 


19 

A  study  of  the  topography  of  the  south  Farallon  island,  on  the  southwest  side 
of  which  the  signal  is  placed,  shows  that  all  the  land  on  the  north,  northwest  and 
west  is  much  higher  than  the  site  of  the  signal.  A  little  east  of  north  from  the 
station  is  the  highest  peak,  on  which  at  an  elevation  of  243  feet  is  the  light- 
house. On  the  west  of  the  eastern  end  of  the  irregular  rock  called  Indian  Head, 
(which  is  only  separated  from  the  main  rock  by  a  narrow  channel),  the  land  rises  to 
225  feet  above  the  sea,  and  the  whole  south  shore  line  of  both  rocks  forms  a  barrier 
to  the  sound  of  the  signal  and  prevents  it  from  reaching  to  the  north  and  west. 

In  endeavoring  to  apply  the  result  of  observations  made  on  this  coast  in  ref- 
erence to  the  audibility  of  fog  signals,  the  position  and  surroundings  of  many  have 
been  studied  by  the  writer,  and  a  brief  discussion  of  such  will  be  of  interest,  taking 
them  in  their  order  from  San  Diego  northward. 

SAN   DIEGO  BAY. 

This  port,  but  a  little  north  of  the  boundary  line  between  Mexico  and  the 
United  States,  enjoys  almost  perfect  immunity  from  fogs  and  thick  haze.  The 
reason  is  not  difficult  to  determine  ;  the  prevalence  of  clear  weather  (the  average 
number  of  clear,  fair,  and  cloudy  days  during  the  year  for  sixteen  years  being  : 
clear,  186  ;  fair,  138  ;  cloudy  and  foggy,  46  ;  )  is  due  to  the  fact  that  the  prevail- 
ing (westerly)  winds  are  comparatively  warm,  the  cooler  winds  coming  from  the 
east.  The  relative  humidity  (per  cent.)  in  the  atmosphere  is  71. 1,  and  there  are 
no  cold  currents  of  air  sweeping  in  to  render  this  amount  of  moisture  visible  to 
any  extent.  There  exists,  therefore,  in  the  neighborhood  of  this  port  perhaps  no 
necessity  for  any  other  sound  signals  than  the  whistling  buoy  now  in  position  on 
the  outside  bar,  near  the  northeast  side  of  the  thick  field  of  kelp  lying  along  the 
western  shore  of  Point  Loma,  and  about  three-quarters  of  a  mile  from  the  Point, 
and  a  like  signal  off  Ballast  Point.  The  kelp  itself  is  an  excellent  indication  of 
the  position  of  the  Point,  but  as  in  dark  nights  it  cannot  be  seen,  the  whistling 
buoy  should  be  carefully  listened  for.  It  has  been  noticed  that  at  times  this 
whistle  cannot  be  heard  at  any  distance,  but  as  a  rule  it  can  be  depended  upon  to 
give  warning  in  time. 

POINT   FERMIN. 

The  next  fog  signal  now  in  position  is  a  bell  buoy  in  Wilmington  Roads,  in- 
side of  Point  Fermhi  light.  It  is  placed  about  three-eighths  of  a  mile  S.  E.  from 
"  Deadman's  Island,"  part  of  the  harbor  of  San  Pedro.  Of  course  the  bell  can- 
not be  heard  but  a  short  distance  off,  and  from  S.  E.  to  S.  W.,  and  not  at  all 
to  the  N.  or  W.  of  the  Point.  In  view  of  the  fact  that  San  Pedro  is  the  port  of 
shipment  for  L,os  Angeles  and  the  region  about  there  and  Anaheim,  and  that  in 
consequence  there  is  double  the  amount  of  shipping  calling  there  that  there  is  at 
any  other  port  south  of  San  Fraucisco,  it  has  been  decided  that  there  shall  be  a  fog 
signal — either  a  steam  whistle  or  siren — erected  on  Point  Fermin  so  as  to  be  heard 
from  W.  to  E.  by  way  of  S. 

West  (Mag.)  from  Point  Fermin  and  about  seven  miles  distant  is  Point  Vin- 
cent. Vessels  coming  down  from  the  northward,  after  leaving  Point  Conception 
make  Point  Vincent  first,  and  as  there  is  considerable  fog  found  in  this  vicinity, 
it  is  desirable  that  a  whistling  buoy  should  be  placed  off  the  point. 


20 


POINT  CONCEPTION. 


The  fog  signal  at  Point  Conception  is  located  on  the  extremity  of  a  plateau 
of  land  extending  some  distance  out  from  the  bluff  behind  it. 


Ft  Conception 


Coxo 


View,  Pt.  Concepcion  bearing  Why  S.  (Compass  )   3  miles 


As  has  been  previously  noted,  fog  prevails  in  the  vicinity  of  this  point  al- 
most continuously  during  the  summer  season.  It  generally  moves  in  from  the 
sea  and  is  more  prevalent  at  night  than  during  the  day.  though  it  is  a  matter  of 
record  that  for  six  weeks,  with  clear  days  and  nights  on  the  point  itself,  the  islands 
on  the  south  side  of  Santa  Barbara  channel  have  been  invisible.  The  same 
authority  (the  Pacific  Coast  Pilot)  says  :  "It,"  Point  Conception,  "  has  been  justly 
and  appropriately  termed  the  '  Cape  Horn  '  and  the  '  Hatteras  '  of  the  Pacific,  on 
account  of  the  heavy  northwesters  that  are  here  met  with.  *  *  with  a  great 
change  of  climate  and  meteorological  conditions,  the  transition  being  remarkably 
sudden  and  well  defined." 

These  changes  are  due  in  a  great  measure,  no  doubt,  to  the  abrupt  change 
in  the  direction  of  the  coast  line,  which  from  the  point  runs  about  due  east,  form- 
ing nearly  a  right  angle  with  the  general  trend  of  the  coast  north  of  the  point,  and 
also  from  the  striking  change  in  the  topography  of  the  country  northeast  of  the 
Santa  Inez  and  San  Rafael  ranges  of  mountains  where  the  dry,  superheated  desert 
plains  approach  nearer  the  coast  than  elsewhere  in  the  State,  and  the  hot  air  from 
these  arid  areas  reaches  the  sea  without  much  change  in  its  temperature.  (Prof. 
Davidson  reports  that  on  one  occasion  such  a  current  Of  heated  air  from  the  north- 
east raised  the  temperature  to  such  a  degree  as  to  destroy  animal  life  and  ruin 
gardens  and  fruit;  and  this  was  followed  by  as  sudden  a  lowering  of  the  tempera- 
ture, the  thermometer  falling  over  fifty  degrees  in  a  few  hours.)  During  the  month 
of  July,  August,  and  September  observers  have  frequently  experienced — generally 
at  night — hot  blasts  of  air  coming  down  from  the  mountains.  These  bodies  of 
air  would,  necessarily,  dissipate  any  fogs  that  might  be  moving  in  from  the  sea, 
and  at  the  same  time  materially  increase  the  evaporation.  As  the  warm 
current — heavily  moisture  laden — moved  further  out  to  sea  however,  it  would 
meet  the  cooler  currents  blowing  in  on  the  land,  and  there  would  be  found  the 
"wall"  of  fog  so  frequently  seen  in  that  locality  off  shore.  Then,  too,  this  cur- 
rent of  warm  air  would  form,  as  has  been  noted  by  Prof.  Henry,  upward  currents 
of  air  and  these  would  tend  to  deflect  the  sound  waves  of  the  signal  on  Point  Concep- 
tion upward,  in  which  case  there  would  probably  exist,  within  a  short  distance  of 
the  fog  signal  an  area  of  inaudibility,  or  the  sound  might  be  reflected  back  from 


21 


the  advancing  wall  of  fog,  and,  in  such  an  event  the  sound  would  not  be  heard  at 
all  on  a  vessel  approaching  the  unseen  danger. 

POINT   ARGUEIXO. 

This  is  the  first  headland  northwest  of  Point  Conception,  from  which  it  is 
distant  12  miles.  It  is  said  to  be  the  foggiest  point  on  the  whole  coast  south  of 
Humboldt,  and  projects  considerably  west  of  Conception.  One  and  a  quarter  miles 
W.  S.  W.  (magnetic)  of  the  point  is  a  second-class  whistling  buoy  which  can  be 
passed  on  either  side.  There  is,  generally,  a  heavy  swell  setting  on  to  this  point 
from  the  W.  and  S.  W.,  and  it  is  probable  that  this  would  tend  to  deflect  the 
sound  of  the  whistle  upward — throw  it  into  the  air — and  so  produce  an  area  of 
inaudibility  in  its  immediate  neighborhood.  Immediately  behind  the  point  there 
is  a  low  semi-circular  basin  lying  at  the  bold  western  end  of  the  San  Rafael  range 
of  mountains,  and  in  this  heated  area  strong  currents  of  air  enter  from  every  direc- 
tion. As  at  Point  Conception  there  are  constant  and  rapid  changes  in  the  atmos- 
pheric temperature,  the  upwrard  ascending  currents  of  hot  air  inducing  cooler  cur- 
rents— laden  with  visible  moisture — to  move  in  from  the  sea. 


£^ 


POINT   SAN    L,UIS. 

After  leaving  Point  Arguello  the  coast  line  runs  about  north  to  Point  San 
Luis,  and,  midway,  Point  Sal  shows  as  an  important  headland.     There  is  no  fog 


22 

signal  off  this  point,  though  fog  prevails  to  a  considerable  extent  in  that  vicinity, 
generally  covering  the  point  and  extending  across  to  the  northward,  as  far  as 
Point  San  Luis.  It  would  be  a  valuable  aid  to  navigators  if  there  was  an  auto- 
matic buoy  off  Point  Sal. 

POINT   SAN    LUIS,    PORT    HARFORD. 

Until  lately  a  second-class  whistling  buoy  has  been  in  position  off  Point  San 
Luis  in  fourteen  fathoms  of  water.  Since  the  discovery  and  location  of  a  new 
danger — a  rock  (which  has  been  named  Souze  Rock)  having  but  16  feet  10  inches 
of  water  over  it  at  low  tide — lying  S.  E.  by  S.  (magnetic)  one  and  three-quarter 
miles  off  Port  Harford  wharf,  and  about  a  half  a  cables  length  inside  of  the  course 
from  Port  Harford  to  Point  Arguello — the  whistling  buoy  has  been  moved  to  a 
point  S.  S.  W.  (magnetic)  and  240  feet  from  the  danger. 

A  steam  whistle  will  soon  be  in  operation  on  Point  San  Luis.  By  reference  to 
the  cut  given  of  the  Point,  it  will  be  seen  that  the  shore  line  is  bold  and  rocky, 
the  land  rising  steeply  to  an  elevation  of  a  little  over  700  feet,  to  the  point  called 
San  Luis  Hill.  A  short  distance  north  of  the  point  is  the  site  called  "  Whaler's 
Flag  Staff,"  and  close  to  this  is  the  station  (x)  where  it  is  intended  to  erect  the 
fog  signal  (a  10-iuch  steam  whistle  probably).  The  position  designated  has  been 
chosen  by  Major  Huer,  Engineer  Corps,  U.  S.  A.,  in  charge  of  this  district,  as 
meeting  the  exigences  of  the  situation  as  satisfactorily  as  any.  It  is  desirable  that 
the  signal  should  be  so  placed  as  to  be  heard  as  far  as  possible  in  the  direction  of 
Point  Buchon  (about  eight  miles  north  of  Point  San  Luis) — i.  e.  along  the  coast — 
where  fogs  prevail,  and  at  the  same  time  to  insure  its  being  heard  to  the  best  ad- 
vantage by  vessels  making  Port  Harford. 

The  projected  location  of  the  signal  (about  40  feet  above  the  sea)  while  suffi- 
ciently elevated  to  place  it  above  the  danger  of  its  being  washed  away  is  low 
enough  to  avoid  the  other  danger  of  its  sound  being  dispersed  in  the  small  valleys 
that  seam  the  high  laud  in  the  vicinity  of  the  point.  "Whaler's  Island"  has 
been  advocated  by  some  as  the  proper  point  for  this  signal  station,  but  was  aban- 
doned as  not  affording  proper  facilities  for  obtaining  fresh  water,  and  as  possessing 
no  advantages  as  regards  the  spread  of  sound  over  the  site  now  determined  upon. 
In  discussing  the  physical  peculiarities  of  Points  Conception  and  Arguello,  Mr. 
Stehman  Forney,  Assistant,  U.  S.  Coast  and  Geodetic  Survey,  called  attention  to  the 
abrupt  change  in  the  direction  of  the  coast  line  at  this  point  as  having  an  important 
effect  upon  the  climate  in  that  vicinity.  When  the  trade  winds  are  blowing  down  the 
line  of  the  coast  (which  they  do  for  the  greater  part  of  the  year)  they  pass  Point 
Conception  and  continue  on  the  line  of  the  islands  lying  south  of  the  point.  Their 
action  in  this  respect  influences  largely  the  direction  and  temperature  of  the  sur- 
face currents,  that  flow  on  to,  and  are  diverted  by  the  islands,  the  effect  being 
to  produce  on  the  Santa  Barbara  coast  a  warm  area  in  which  fogs  rarely  prevail 
close  in  shore.  But  this  same  warm  reflex  current  evaporates  a  large  amount  ot 
moisture  that,  meeting,  a  short  distance  out  from  the  land,  the  cool  air  moving  in 
from  the  sea,  produces  fog  which  prevails  for  long  periods  of  time.  During 
thirteen  consecutive  weeks,  Mr.  Forney  adds,  while  at  work  in  the  vicinity  of 
Piedras  Blancas  and  Point  Sal,  he  did  not  see  the  shore  line  once,  the  fog  hanging 


23 

over  it  to  a  height  of  1300  or  1400  feet.  This  bank  often  simulates  the  contour 
of  the  land  to  a  remarkable  degree,  and,  though  sometimes  30  to  40  miles  distant 
(off  shore)  the  resemblance  to  the  coast  line  is  so  striking  as  to  completely  deceive 
captains  of  vessels  bound  in. 

The  San  Bernardino  channel  is  a  great  thoroughfare,  the  track  for  all  coasters 
southward  bound  being  through  it.  For  this  reason,  as  well  as  from  the  fact  that 
many  deep  sea  vessels  make  Point  Conception  in  approaching  the  coast,  it  is 
desirable  that  a  light  and  fog  signal  should  be  placed  on  San  Miguel  island,  the 
northernmost  of  the  chain  bounding  the  channel  on  the  W.  and  S.  W.  Such 
signals  have  already  been  asked  for  by  Col.  L,udlow,  U.  S.  N.,  the  inspector  in 
charge  of  the  district. 

POINT    PIEDRAS    BLANC  AS. 

Continuing  northward  the  next  fog  signal  (a  whistling  buoy)  is  in  position 
off  Point  Piedras  Blancas,  (incorrectly  spelled  Pedros  Blancos  on  page  4)  and  still 
further  northward  is  another  ' '  whistler ' '  off  Point  Sur. 

In  the  vicinity  of  this  latter  signal  there  occurs  some  peculiar  phenomena  in 
connection  with  the  audibility  of  the  signal.  It  is  the  experience  of  many  navi- 
gators that  the  whistling  buoy  located  there  is  (generally)  heard  plainer  to  wind- 
ward than  to  leeward. 

The  position  of  this  signal  with  reference  to  the  point  is  peculiar.  The  whistle 
is  located  S.  W.  by  W.  and  a  little  less  than  one  nautical  mile  from  the  point  in 
26^  fathoms  of  water.  The  shore  line  north  of  the  point  runs  approximately 
north,  with  the  "  10  fathom  line"  parallel  to  it  and  from  one-fourth  to  five-eighths 
of  a  mile  distant.  On  this  shore  the  sea  breaks  heavily  at  all  times.  The  swell 
setting  in  from  the  westward  is  very  uniform,  and  vessels  passing  the  point  would 
be  running — for  the  most  part — in  the  trough  of  these  long  undulations.  It  has 
been  conjectured  that  the  sound  waves  from  the  whistle  would  be  carried  in  these 
troughs  to  a  considerable  distance,  and  that  they  would  not  be  so  seriously  affected 
by  the  wind  as  would  sound  waves  emanating  from  a  source  higher  above  the  sea 
level. 

South  of  the  point  the  coast  curves  toward  the  S.  E.  for  several  miles,  and  in 
the  bight  thus  formed  are  found  masses  of  kelp,  numerous  small  shoals,  and  rocks, 
while  the  "  10  fathom  line,"  pursuing  a  south  course  from  the  point,  at  two  miles 
south  of  the  point  is  found  a  mile  and  a  quarter  off  the  shore.  The  presence  of 
the  kelp,  shoals,  etc.,  indicate  a  reflex  current,  or  eddy,  of  considerable  extent 
south  of  the  point,  and  the  influence  of  the  change  in  the  direction  of  the  general 
set  of  the  surface  currents  would  undoubtedly  affect  the  audibility  of  the  signal 
placed,  as  this  one  is,  a  little  north  of  this  disturbance. 

The  topography  of  the  point  is  peculiar.  It  presents,  toward  the  sea,  a  bold 
front,  curved  in  towards  the  center,  and  in  its  general  shape  suggesting  a  concave 
reflector.  The  whistling  buoy  is  almost  exactly  opposite  the  center  of  this  surface, 
and  less  than  a  nautical  mile  from  it.  From  point  to  point  of  this  curved  surface  is 
something  more  than  a  quarter  of  a  mile,  and  it  is  reasonable  to  infer  that  the 
sound  of  the  whistle  will  be  reflected  from  this  bold  shore  to  a  considerable  dis" 


24 

tance.  If  such  be  the  case,  the  probabilities  are  that  the  signal  would  be  heard 
most  intensely  in  a  S.  W.  direction  from  the  point  in  ordinary — and  especially  in 
calm — weather. 

There  will  soon  be  placed  in  position  on  this  point  a  steam  signal  which  will 
be  of  great  help  to  navigators. 

POINTS   PINOS   AND   SANTA   CRUZ. 

Point  Pinos — forming  the  southwest  point  of  Monterey  Bay,  and  Point  Santa 
Cruz  its  northwest  point,  are  very  nearly  twenty  miles  distant  from  each  other, 
and  are  both  provided  with  fog  signals  (whistle  buoys).  Foggy  weather  frequently 
prevails  in  the  bay,  and  in  former  years  vessels  were  guided  in  by  the  firing  of  a 
gun  in  response  to  a  like  signal  from  the  approaching  vessel.  At  the  present 
time  during  foggy  weather  the  whistlers  should  be  listened  for  carefully,  and  in 
addition  the  lead  be  kept  going.  Not  unfrequently  the  sound  of  the  surf  breaking 
on  the  beach  can  be  heard  to  a  considerable  distance. 

ANO   NUEVO. 

Eighteen  miles  from  Point  Santa  Cruz  the  shore  line  curves  well  to  the  west- 
ward and  southwest,  forming  Point  Ano  Nuevo.  In  coming  from  the  southward 
steamers  try  to  make  this  point,  and  to  indicate  its  position  there  is  located  here 
a  steam  whistle  as  well  as  a  light.  During  foggy  weather  this  whistle  is  sounded 
for  10  seconds,  at  intervals  of  55  seconds. 

At  this  station,  which  is  six  miles  south  of  Pigeon  Point,  some  experi- 
ments have  been  made  that  indicate  an  area  of  inaudibility  as  existing  not  far 
from  the  whistle.  The  steamer  Shubrick,  in  1875-76,  was  run  in  three  different 
directions  from  the  signal  during  the  existence  of  fog,  while  the  whistle  was  regu- 
larly blown  all  the  time.  Captain  Korts,  in  charge  of  the  vessel,  says  that  in 
running  in  a  northwest  direction  straight  from  the  signal  and  to  windward,  the 
sound  was  heard  up  to  near  the  third  mile  and  then  lost,  and  regained  at  four 
miles  distance.  In  running  southeast — i.  e.  with  the  wind — the  sound  was  lost 
near  the  second  mile,  and  was  not  heard  again  until  the  fourth  mile  was  reached. 
In  moving  straight  out  from  shore,  in  a  southwest  course,  the  sound  was  heard 
continuously  during  the  whole  four  miles.  The  fog  in  those  trials  did  not  reach 
more  than  150  feet  above  the  surface  of  the  ocean,  and  upon  going  to  the  mast- 
head, Captain  Korts  found  that  immediately  over  the  signal  it  was  swelled  up  in 
an  umbrella-like  shape,  and  was  very  thin  at  the  summit  of  this  dome,  the  steam 
from  the  whistle  showing  through  it. 

These  experiments,  as  well  as  the  experience  of  Capt.  Whitelaw  already 
quoted,  indicate  that  when  sound  signals  are  generated  in  one  medium,  whether 
that  be  a  clear  atmosphere  or  a  more  or  less  dense  fog,  the  sound  waves  have  great 
difficulty  in  passing  from  that  media  to  another. 

An  examination  of  the  diagram  given  on  page  10  shows  that  at  all  seasons  of 
the  year  fog  prevails  to  a  considerable  extent  at  Ano  Nuevo  and  Pigeon  Point,  six 
miles  further  north,  and  is  in  excess  of  the  amount  indicated  in  the  vicinity  of 
Point  Montara.  The  character  of  the  country  changes  somewhat  suddenly  north 
of  Pigeon  Point  and  Montara,  the  high  ranges  terminating  in  a  peak  2,000  feet 
high,     The  fog  almost  alway  hangs  about  this  peak,  and  whereas  the  mountains 


25 

of  the  peninsula  up  to  the  viciuit)^  of  this  point  are   clothed  with  redwood  trees, 
this  growth  terminates  here,  and  is  not  seen  again  south  of  San  Francisco. 

It  has  been  frequently  noticed  by  masters  of  vessels  running  on  this  coast 
that  when  four  miles  S.  W.  from  the  Aho  Nuevo  signal,  the  whistle  could  only 
be  heard  very  faintly,  and  this  during  calm  weather.  When  abreast  of  the  whis- 
tle it  is  heard  distinctly.  The  same  thing  has  been  noticed  at  Pigeon  Point.  At 
Ano  Nuevo  there  is  a  smoke  stack  in  front  of  the  whistle,  but  it  is  not  likely  that 
this  interferes  with  the  audibility  of  the  signal,  as  experience  has  shown  that 
the  sound  waves  when  encountering  an  obstacle  of  that  description  are  united 
again  within  a  very  short  distance.. 

POINT  LOBOS. 

This  point,  marking  the  southern  side  of  the  entrance  to  San  Francisco  Bay,  is 
essentially  different  in  conformation  from  the  opposite  point — Boneta.  The  '"Seal 
Rocks  ' '  off  the  Point  have  behind  them  a  range  of  low  sand  hills,  while  Boneta 
rises  rocky  and  bold  to  nearly  300  feet  elevation,  with  still  higher  land  behind  it. 

In  former  years,  before  the  establishment  of  any  fog  signals  on  this  coast, 
captains  of  vessels  making  the  harbor  of  San  Francisco  during  foggy  weather 
usually  ran  in  until  they  could  hear  the  seals  barking  on  the  rocks  off  Point 
Lobos,  and  then  shaped  their  course  for  the  vicinity  of  Mile  Rock,  and  so  into 
the  channel  and  through  the  Gate.  Even  now  the  peculiar  cry  of  these  creatures 
is  a  valuable  guide  to  mariners  in  times  of  fog,  and  for  the  good  service  they 
have  done  as  "fog  signals"  our  pilots  and  ship  masters  protest  against  their 
being  destroyed,  as  has  been  advocated  by  fishermen ^and  others. 

The  fog  moving  in  to  the  bay  of  San  Francisco  has,  generally,  an  apparent  direc- 
tion over  Point  Iyobos  and  the  hills  behind  it,  and  so  diagonally  crossing  the 
' '  Gate ' '  itself,  covering  Fort  Point,  will  stretch  across  to  Alcatraz  and  Angel 
Island,  leaving  L,ime  Point  and  the  Tamalpais  shore  clear.  Amongst  the  sand 
hills  on  the  south  shore  the  curious  phenomena  is  seen  of  the  fog  capping  the 
rounded  tops  of  these  hills  while  the  valleys  between  are  clear.  This  is  due  prob- 
ably to  the  presence  of  a  layer  of  warmer  air  in  the  hollows  (where  the  sun's  rays 
are  more  concentrated)  that  evaporates  the  moisture  or  more  properly  separates 
the  watery  vesicles  so  that  they  are  rendered  invisible. 

Tne  Pacific  Coast  Pilot,  page  69,  has  the  following  in  regard  to  summer  fogs  : 
"  From  April  to  October  inclusive  the  prevailing  wind  is  from  the  North  West. 
During  the  summer  the  wind  sets  in  strong  about  10  A.  m.,  increasing  until  nearly 
sunset  when  it  begins  to  die  away.  During  its  height  it  almost  regularly  brings 
in  a  dense  fog,  which,  working  its  way  over  the  peninsula,  meets  that  already 
advanced  through  the  Golden  Gate,  and  envelops  San  Francisco  and  the  bay  by 
sunset.  As  a  rule  the  breeze  does  not  dispel  the  fog.  If  a  fog  exists  outside,  the 
wind  is  sure  to  bring  it  in.  but  the  heated  earth  dissipates  it  for  a  time." 

"  High  "  fogs  are  particularly  noticeable  about  Point  Diablo,  and  it  is  in  this 
vicinity  that  the  difference  between  fogs  produced  over  the  land  and  those  origin- 
ating out  at  sea  is  particularly  noticeable.  The  former  are  more  of  the  nature  of 
true  "clouds,"  being  dense  and  snowy  white,  rolling  down  in  rounded  masses, 
with  clear  intervals  between,  while  the  latter  range  from  light  grey  to  what  is 


26 

called  "  black  fog,"  in  color.  The  latter  occurs,  too,  more  in  horizontal  layers, 
and  its  apparent  motion  is  more  progressive  than  the  former,  which,  as  has  been 
said,  rolls  down  from  the  hills  and  settles  upon  the  water,  or  a  short  distance 
above  it,  like  a  fleecy  cover. 

It  is  this  latter  fleecy  white  fog  that  is  the  most  dreaded  by  masters  and  pilots 
of  vessels  in  the  bay  of  San  Francisco.  While  the  gray  sea  fog  is  troublesome 
enough,  the  other  is  often  so  dense  as  to  prevent  anything  from  being  seen  more 
than  a  few  (sometimes  not  more  than  eight  or  ten)  feet  distant. 

The  phenomena  presented  of  two  transparent  media — air  and  water — in 
combination,  intercepting  the  rays  of  light  so  as  to  prevent  their  passage  is  a  per- 
plexing one.  There  has  been  no  satisfactory  explanation  offered  of  it,  though  the 
most  plausible  theory  is  that  the  aqueous  vesicles  suspended  in  the  atmosphere  dis- 
perse the  rays  of  light  in  many  different  directions,  and  so,  practically,  absorb 
them.  In  what  is  called  "  black  "  fog,  this  absorption  is  complete;  in  other  words, 
the  mass  of  combined  aqueous  vapor  and  air  cut  off  all  the  rays.  Masses  of 
"white  "  fog  seem  to  be  entirely  filled  with  diffused  light,  and  to  permit  a  portion 
to  pass  through  or  be  reflected  from  all  parts  of  their  surfaces.  Those  who  have 
noticed  at  night  the  vapor  ejected  from  a  locomotive  while  the  machine  is  working 
powerfully  drawing  a  train  up  a  steep  grade,  have  seen  the  partially  condensed  steam 
from  the  exhaust  converted  into  clouds  of  snowy  white  vapor  when  illuminated 
by  a  strong  light  such  as  the  "  head  light "  of  the  engine,  and  witnessed  the  phe- 
nomena of  the  total  absorption  of  the  light  so  that  the  vapor  casts  a  distinct  shadow 
as  it  floats  away.  But  when  the  light  happens  to  traverse  the  jet  of  superheated 
steam  escaping  from  the  safety  valve,  it  passes  through,  and,  until  the  steam  is 
cooled  somewhat,  there  is  no  shadow.  The  conclusion  arrived  at  is  that  the  power 
possessed  by  air  to  intercept  or  disperse  rays  of  light  depends  upon  the  presence 
of  a  certain  proportion  of  aqueous  vapor  in  it,  and  the  size  of  the  vesicles.  Up  to 
a  certain  point  in  the  growth  of  these  vesicles  the  power  increases  until  the  propor- 
tion of  aqueous  vapor  is  such  that  it  exists  as  rain;  when  the  dispersion  of  the 
rays  of  light  produces  the  rainbow  and  then,  practically,  ceases. 

POINT   BONETA   AND   LIME   POINT. 

Many  of  the  peculiarities  attendant  upon  the  audibility  of  the  fog  signals  on 
Point  Boneta  and  Lime  Point  have  been  previously  discussed  in  connection  with 
the  diagram  of  the  entrance  to  the  Golden  Gate.  There  might  be  much  more 
written  on  this  subject,  but  enough  has  been  said  to  indicate  that  a  series  of  sys- 
tematic experiments  on  the  audibility  of  sound  signals,  carried  on  in  this  vicinity, 
could  not  fail  to  be  of  great  interest  and  importance. 

The  facilities  existing  in  that  vicinity  for  conducting  such  experiments  are 
very  great.  All  of  the  conditions  that  effect  the  sound  of  signals  are  to  be  found 
there,  and  the  importance  of  their  study  cannot  be  overestimated. 

The  Lime  Point  whistle  has  great  penetrative  power,  it  having  been  heard 
outside  the  bar  for  not  less  than  ten  to  twelve  miles.  In  this  connection  it  may 
be  remarked  that  the  efficiency  of  sound  signals  depends,  in  a  very  great  degree, 
upon  this  ' '  power  of  penetration  ' '  possessed  by  the  sound  of  the  instrument,  and 


27 

that  often  a  small-sized  signal  having  this  peculiar  power  is  more  effective  than 
larger  ones  whose  tones  are  without  this  sonorous  characteristic. 

FOG   BELL   AT   FORT   POINT. 

The  fog  bell  at  Fort  Point  is  located  at  forty  feet  elevation  above  the  water. 
During  fogs  it  is  struck  every  ten  seconds,  and  should  be  heard  for  a  mile  or  a 
little  more,  perhaps.  In  point  of  fact  it  is  said  to  be  hardly  ever  heard  except 
when  too  late  to  be  of  use.  It  is  not  to  be  inferred  from  this  that  wrecks  have  oc- 
curred because  this  bell  was  not  heard  in  time,  but  that  if  mariners  depended  upon 
its  sound  to  tell  them  how  near  they  were  to  the  point,  they  would  generally  have 
no  time,  after  hearing  it,  to  clear  the  danger.  This  inaudibility  of  the  Fort  Point 
bell  is  due  to  several  causes.  In  the  first  place  the  prevailing  winds  tend  to  carry 
its  sound  directly  away  from  incoming  vessels,  and  it,  has  been  proven  that  the 
sound  of  bells  have  very  little  penetrative  force  against  the  wind — not  near  so 
much  as  sirens  and  steam  whistles. 

Then,  the  peculiar  manner  in  which  the  heavy  sea  fogs  advance  into  the  Golden 
Gate,  tends  to  check  the  progress  of  sound  waves  meeting  them.  Presenting,  as 
it  often  does,  a  wall-like  front  across  the  entrance,  outside  of  a  line  from  Fort 
Point  to  Point  Diablo,  the  sound  of  the  bell  on  Fort  Point  is  thrown  back  or  ab- 
sorbed by  the  vapor,  and  so  is  not  to  be  heard  within  the  body  of  fog. 

A  third  cause  of  inaudibility  is  the  rapid  and  varying  currents  in  the  chan- 
nel, produced  by  the  ebb  and  flow  of  the  tide,  as  experience  has  proven  that  sound 
signals  cannot  be  heard,  usually,  with  normal  distinctness  when  a  rapid  stream  is 
flowing  between  the  observer  and  the  signal,  especially  when  the  current  and 
wind  run  in  opposite  directions. 

The  accumulation  of  evidence  in  regard  to  the  efficiency  of  bells  as  fog  sig- 
nals is  to  the  effect  that  they  are  of  but  little,  if  any,  use.  Bells  of  2^  tons 
weight,  struck  every  4  minutes  by  a  60-lb  hammer  falling  10  inches  (at  Houth, 
England)  were  heard  only  one  mile  to  windward,  against  a  light  breeze,  during  fog. 

Mr.  Cunningham,  speaking  of  bells  in  fog  at  Bell  Rock,  and  Skerrymore 
Lighthouse  (England)  says  he  doubts  if  a  single  vessel  has  been  saved  by  them 
in  fog.  He  does  not  recall  a  single  instance  of  where  a  vessel  put  about  in  a  fog 
from  hearing  a  bell. 

General  Duane  (of  the  U.  S.  Lighthouse  Board)  says  a  bell  cannot  be  consid- 
ered an  efficient  fog  signal  on  the  sea  coast. 

ANGEL    ISLAND,  SAN  FRANCISCO  HARBOR. 

On  the  S.  W.  extremity  of  Angel  Island  is  placed  a  bell  that  in  time  of  fog  is 
struck  a  double  blow  every  fifteen  seconds.  Experiments  made  with  this  bell,  as 
well  as  with  signals  blown  by  the  whistle  of  steam  vessels  stationed  near  the  bell, 
show  that  the  sounds  are  strongly  ' '  echoed  ' '  from  the  Saucelito  shore,  and  that  ob- 
servers on  vessels  in  mid-channel  between  the  two  shores  would  be  apt  to  refer  the 
source  of  such  signals  to  the  latter  shore.  A  careful  study  of  the  contour  of  the 
high  land  behind  the  Angel  Island  bell,  and  the  hills  that  confront  it  on  the  op- 
posite (Saucelito)  shore,  shows  that  the  two  combined  include  an  area  well  calcu- 
lated to  develop  echoes.  The  bell  on  Angel  Island  is  so  located  that  the  residents  on 
the  opposite  shore  should  hear  it  very  distinctly,  while,  during  the  prevalence  of 


28 

the  dense  white  fog  so  commonly  seen  in  the  channel,  an  observer  in  the  fog 
might  not  hear  it  at  all.  If  vessels  passing  up  or  down  between  the  two  points  men- 
tioned keep  on  the  east  side  of  the  channel,  they  may  be  reasonably  sure  of  picking 
up  the  Angel  Island  bell  in  its  own  focus  of  sound,  which,  theoretically,  is  found  to 
exist  about  half  a  statute  mile  from  the  signal. 

Masters  of  vessels  coming  down  from  San  Quentin  in  foggy  weather  very 
seldom  hear  the  bell  located  on  Alcatraz  island.  This  is  no  doubt  due  to  pre- 
vailing winds  blowing  towards  the  signal. 

MARKET  STREET   WHARF   BELL. 

The  pilot-captains  of  the  ferryboats  running  between  San  Francisco  and  Oak- 
land, have  had  occasion  to  note  an  interesting  fact  in  connection  with  this  signal.  It 
has  been  observed  by  them  that  when  leaving  the  San  Francisco  slip  in  time  of  fog, 
the  sound  of  the  bell  on  the  end  of  the  pier  is  heard  distinctly  until  the  observer 
has  reached  a  point  about  equi-distant  between  the  bell  and  the  south  shore  of 
Yerba  Bueua  (Goat)  Island,  when  the  sound  is  lost  for  a  time,  and  again  heard 
when  the  observer  is  near  the  island,  its  sound  coming,  apparently,  from  the  island 
itself.  There  are  a  number  of  causes  that  operate  to  produce  this  effect,  amongst 
which  is  the  presence  of  a  strong  tidal  current,  flowing,  when  the  tide  is  making, 
past  North  Point  and  so  along  the  city  front  at  nearly  right  angles  to  the  track  of 
the  boat  crossing  to  Oakland.  (This  current  is  often  strong  enough  to  render  the 
approach  of  the  ferry  boats  to  their  slips  at  the  foot  of  Market  street  a  matter  of 
nice  calculation,  though  since  the  wharf  at  the  foot  of  Greenwich  street  has  been 
extended  it  has  been  thrown  out  so  that  there  is  now  but  little  current  inshore 
south  of  the  wharf  for  500  feet  out.)  This  cross-current  undoubtedly  interferes 
with  the  sound  waves  from  the  bell  crossing  it.  Again,  as  the  bell  is  raised  but  a 
few  (perhaps  fifteen)  feet  above  the  surface  of  the  water,  its  sound  waves  in  pass- 
ing over  this  surface  would  be  deflected  by  the  planes  of  surface  produced  by 
winds,  currents,  and  in  the  wake  of  the  boats  themselves,  in  maii}r  different  direc- 
tions, the  general  effect  being  to  send  them  into  the  air,  to  be  lost  until  impinging 
on  the  bold  south  shore  of  Yerba  Buena  Island,  they  are  thrown  back  toward  the 
approaching  vessel  to  be  heard  again. 

There  is  a  peculiar  condition  of  fog  prevailing  at  times  in  the  vicinity  of  the 
channel  or  lane  in  which  the  ferry  boats  spoken  of  are  obliged  to  run.  That  is, 
it  sometimes  happens,  that  a  thick  bank  of  dense  white  vapor  will  extend  across 
the  bay,  covering  the  area  spoken  of,  while,  on  either  side,  within  a  short  distance, 
the  atmosphere  is  clear.  It  was  in  such  a  local  bank  that  the  ferry  boats  Ala- 
meda and  Capitan  collided  a  few  years  ago.  At  that  time  the  Pilot  Captain  of 
the  Capitan  states  that  the  whistles  of  both  boats  were  sounded,  and  that  imme- 
diately after  hearing  the  whistle  of  the  Alameda  at,  as  he  thought,  a  half  mile 
distance,  the  vessel  appeared  within  a  few  feet  and  the  collision  took  place.  The 
fog  was  so  dense  then  that  the  bow  of  the  Capitan  was  barely  visible  from  her 
pilot  house,  while  its  vertical  thickness  was  so  small  that  the  top  of  the  smoke 
stacks  of  the  boats  were  above  it.  This  fact  was  particularly  noted  by  the  keeper 
then  in  charge  of  the  fog  signal  on  Yerba  Buena  island.  He  states  that  at  the 
time  of  the  collision  he  could  see   nothing  of  either  vessel  but  the  tops  of  their 


29 

smoke  stacks,  and  that  when  their  whistles  were  blown  the  steam  was  projected 
through  the  upper  surface  and  that  he  could  distinctly  note  the  waves  of  sound 
undulating  in  all  directions  over  the  upper  surface,  and  could  watch  them  until 
they  reached  him  and  were  heard  by  him. 

The  ferry  boats  plying  between  San  Francisco  and  Oakland  have  quite  a  nar- 
row lane  or  fairway  in  which  to  run,  and  this  lane  should  always  be  clear  of  ves- 
sels at  anchor.  But  it  happens  that  vessels  anchor  so  near  to  the  borders  of  this 
lane  that  on  a  change  of  tide  they  swing  partly  into  it.  This  increases  the  dan- 
ger of  collision  in  time  of  fog,  and  ship  masters  should  take  care  not  to  place 
their  vessels  in  such  positions. 

Standing  at  the  mouth  of  one  of  the  small  valleys  in  the  Tamalpais  hills, 
between  Saucelito  and  Lime  Point,  the  sound  of  the  Boneta  siren — distant  three 
miles — is  heard  plainer  than  the  steam  whistle  on  Lime  Point,  less  than  half  a 
mile  away.  Studying  the  configuration  of  the  land  between  Point  Boneta  and 
the  mouth  of  this  valley,  it  will  be  seen  that  the  depression  extends  from  one 
locality  to  the  other.  Hence  the  sound  from  the  Boneta  signal  is  ' '  echoed ' ' 
plainly  to  the  ear  of  the  observer  who  is  stationed  at  the  mouth  of  this  winding 
depression  in  the  hills  that  cuts  off,  on  the  Lime  Point  side,  the  sound  of  the  sig- 
nal at  that  station. 

The  same  reflection  of  sound  is  noticeable,  at  times,  when  fog  prevails  over 
the  city  of  San  Francisco.  The  Boneta  signal  has  then  been  heard  distinctly  when 
the  steam  whistle  on  Lime  Point  has  not  been  heard  at  all,  though  at  least  two 
and  one-half  miles  nearer  the  observers.  This  phenomenon  is  due,  perhaps,  to  the 
peculiar  contour  of  the  sand  hills  on  the  shore  opposite  Point  Boneta.  There 
opens  almost  immediately  in  the  center  of  the  large  curve  described  by  the  bluff 
shore,  a  valley,  which  can  be  traced  back  on  the  peninsula  into  the  city  itself. 
Waves  of  sound  from  Boneta  entering  this  valley  straight  from  the  signal  would 
be  carried,  by  reflection,  to  a  considerable  distance  inland. 

These  instances  are  given  to  illustrate  the  fact  that  where  the  contour  of  the 
land  behind  any  fog  signal  is  flat  or  broken  into  valleys,  much  of  the  sound  is 
lost  landward.  In  the  case  of  the  steam  sirens,  whose  trumpets  are  directed  sea- 
ward, the  percentage  of  loss  is  less  than  in  the  case  of  an  open  steam  whistle. 

Prof.  Henry  of  the  U.  S.  Lighthouse  Board  in  a  report  made  by  him  in  1865 
on  the  subject  of  sound  in  connection  with  fog  signals  says  in  reference  to 
trumpets  directed  seaward,  that  the  sound  was  heard  6  miles  in  front  and  only  3 
miles  in  rear  of  the  mouth  of  the  signal. 

In  1867,  when  there  was  a  "  Daboll  trumpet  "  on  Point  Lobos,  it  was  noticed 
by  Prof.  Davidson,  that  its  sound  was  heard  six  or  seven  miles  to  windward 
against  an  ordinary  N.  W.  wind,  the  weather  being  clear.  No  area  of  inaudibility 
was  noticed  as  the  vessel  on  which  the  observations  were  made  ran  from  the  shore 
seaward. 

The  fog  signal  on  Yerba  Buena  is  not  heard  in  its  full  intensity  until  the  ob- 
server is  directly  opposite  it.  The  conformation  of  the  land  immediately  behind 
this  signal  goes  far  towards  explaining  this.  There  is  a  series  of  hollows  that, 
upon  the  whole,  reflect  the  sound  directly  out  from  the  signal.     Above  the  level 


3° 

ot  the  signal  these  reflecting  surfaces  tend  to  throw  the  sound  toward  the  San  Fran- 
cisco shore  on  the  one  hand,  but  high  above  the  sea,  and  to  cut  them  off  from  the 
range  of  vessels  approaching  the  island  from  the  Oakland  wharves.  Thus  it  hap- 
pens that  the  signal  on  this  island  is  often  heard  distinctly  on  the  heights  back  of 
the  city  front  when  it  is  not  heard  on  the  front  itself.  And  on  the  Oakland  side 
vessels  must,  generally,  be  close  to  the  signal  before  it  is  heard. 

There  is  an  echo  produced  by  the  steam  whistle  on  Pablo  Point  (East  Brother) 
which  is  very  confusing,  and  as  the  flood  tide  is  very  erratic  in  this  locality,  mar- 
iners, in  time  of  fog,  have  to  use  great  care  in  passing  the  point.  The  late 
instance  of  the  steamer  running  between  San  Francisco  and  Mare  Island  being 
"lost"  in  a  fog  off  East  Brother  and,  being  misled  by  the  sound  of  the  signal, 
running  onto  a  mud  bank  and  remaining  there  until  the  fog  cleared  off,  is  a  case  in 
point. 

The  East  Brother  signal  is  almost  always  heard  distinctly  at  Saucileto,  the 
sound  being  carried  through  Raccoon  Straits  between  Angel  Island  and  Tiburon. 

On  pages  8  and  9  the  amount  of  fog  in  the  vicinity  of  Mare  Island  is  given 
as  well  as  its  period  of  duration.  In  reference  to  the  character  and  appearance  of 
fog  in  this  vicinity  and  further  on  in  Suisun  Bay,  Capt.  Louis  A.  Sengteller, 
Ass't  U.  S.  C.  and  G.  Survey,  states  that  during  the  resurvey  of  Suisun  bay  in 
1888,  he  noticed  that  during  the  Spring  and  Summer  a  light  fog  would  hang  over 
the  bay  very  early  in  the  morning  and  be  dissipated  by  the  sun  by  9  o'clock.  Its 
appearance  and  duration  was  different  however  in  October  and  November  at  which 
times  the  fog  prevailed  subsequent  to  rains.  Generally  speaking,  the  fogs  in 
that  region  are  "freshwater"  or  "river"  fogs,  formed  by  the  condensation  of 
the  aqueous  vapor  rising  from  the  waters  of  the  Sacramento  and  San  Joaquin 
being  condensed  by  the  cooler  air  moving  in  from  the  sea.  These  are  "  low  "  fogs, 
having  no  great  density,  and  are  quickly  dissipated.  In  the  Winter  season  they 
are  "  high  "  fogs  lasting,  sometimes,  all  day. 

THE   COAST  LINE   NORTH    OF  SAN    FRANCISCO. 

Leaving  the  harbor  of  San  Francisco  and  going  northward,  it  may  be  men- 
tioned in  this  place  that  since  the  removal  of  the  buoy  formerly  marking  the  mid- 
way in  Boneta  channel,  mariners  approaching  the  point  in  foggy  weather  have 
to  be  doubly  cautious  as  they  are  then  guided  almost  wholly  by  the  sound  of  the 
siren  on  the  point;  and  its  notes  are,  not  seldom,  confusing  as  regards  direction. 

Professor  Davidson  says  that  there  exists  an  area  of  inaudibility  in  Boneta  Chan- 
nel, and  cites  the  instance  of  the  White  Sparrozv  which  struck  on  the  rocks  close 
to  Point  Boneta  while  it  was  foggy,  the  captain  thinking  he  was  on  Mile  Rock. 
This  failure  to  hear  the  signal  was  due,  probably,  to  its  sound  being  thrown  into 
the  air  by  the  strong  wind  which  prevailed,  being  deflected  upward  from  the  bluff 
shore,  on  which  the  signal  is  placed,  and  on  which  the  wind  impigned. 

It  has  been  observed — in  this  connection — that  the  sound  of  the  whistling 
buoy  off  San  Francisco  harbor,  when  approaching  it  from  the  S.  W.,  has  been 
heard  at  a  distance  of  9  miles — in  light  S.  W.  wind — lost  when  within  8  and  7 
miles  and  regained  again  when  within  4  miles. 

Captain  W.  R.  Perriman,  a  veteran  navigator,  who  has  been  running  between 


3i 


San  Francisco  and  the  Hawaiian  Islands  for  the  past  thirty  years,  is  of  the  opin- 
ion that  the  automatic  (whistling)  buoy  is  the  best  signal  now  in  use,  from  the 
fact  that  as  it  is  near  the  surface  of  the  water  it  can  be  heard  further  than  signals  at 
higher  elevations.  At  the  same  time  he  has  noticed  that  the  sounds  from  such 
signals  have  been  ' '  killed ' '  by  intervening  waves.  [This  is  in  accordance  with 
the  theory  that  the  waves  of  sound  are  deflected  upward  by  intervening  swells, 
and  leads  to  the  remark  that  where  such  a  swell  exists  at  right  angles  with  the 
locality  of  the  whistling  buoy  the  mariner  has  calculated  he  is  approaching,  he 
should  be  prepared  to  lose  its  sound.] 

Another  observation  made  by  the  Captain  was  that  when  approaching  Pt. 
Arena  he  has  heard  it  distinctly  while  in  the  cabin  of  the  vessel,  but  could  only 
make  it  out  very  faintly  when  on  deck. 

A  valuable  observation  made  by  Captain  Perriman  is  that  when  within  a 
comparatively  short  distance  of  the  fog  signals — whistles  or  sirens — that  are  actu- 
ated by  steam,  he  has  noticed  a  peculiar  "  drawback"  to  the  sound — as  if  the 
motive  power  was  recovering  its  breath.  This  peculiar  sound  is,  no  doubt,  due 
to  the  fact  of  the  sound  produced  by  the  rushing  in,  behind  the  outward  blast,  of 
the  atmosphere.  This  would  not  be  heard  as  long  as  the  superior  note  of  the  sig- 
nal filled  the  ear,  but  would  be  audible  for  a  moment  or  two  as  soon  as  the  blast 
was  cut  off. 


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POINT   REYES. 

The  fog  signal  at  Point  Reyes  is  located  on  the  extreme  north  point  of  the 
rock-bound  head  terminating  the  north  shore  of  Drake's  Bay.  The  signal  is  190 
feet  above  the  sea,  and  above  it,  at  an  elevation  of  220  feet,  is  the  Point  Reyes 
light.  These  two  aids  to  navigation  are  among  the  most  important  on  the  coast, 
as  most  vessels  coming  into  the  harbor  of  San  Francisco  make  this  point,  coming 
in  between  Point  Reyes  and  the  Farallones. 

When  locating  the  fog  signal  the  present  site  was  chosen  as  being  the  best 
under  all  circumstances.  Still,  as  has  been  said,  the  signal  is  seldom  heard  north 
of  the  point.  There  the  land  trends  away  in  a  long,  low,  barren  beach,  rising 
farther  back  into  undulating  sandy  hills.     There  seems  to  be  no  practical  remedy 


32 

for  this  area  of  inaudibility  north  of  Point    Reyes  station,    except,    perhaps,    the 
establishment  of  another  signal  on  the  southwest  point. 

It  is  a  well  established  fact  that  north  of  Point  Reyes,  even  when  in  the  im- 
mediate vicinity  of  the  signal,  it  can  seldom  be  heard,  though  vessels  deceived  by 
this  phenomenon  have  gone  in  close  enough  during  fog  to  hear  ' '  roosters  crowing 
on  the  land."  Captain  H.  T.  Houdlette,  of  the  O.  S.  S.  Australia,  says  that  in 
coming  on  to  the  coast  and  feeling  his  way  along  in  a  dense  fog,  he  has  caught  the 
loom  of  Noonday  Rock  [12  miles  from  Point  Reyes],  and  gone  in  some  distance 
without  hearing  the  siren,  though  it  was  in  full  blast. 

POINT   ARENA. 

The  next  point  at  which  there  is  a  fog-signal  (Point  Arena)  rivals  Point 
Reyes  in  the  quantity  and  duration  of  fog.  The  local  surroundings  of  the  point 
are  such  that  abberration  of  sound  of  the  signal  can  be  safely  predicted. 

Captain  Sengteller  states  that  while  in  camp  on  Coast  Survey  duty  at  a  land- 
ing called  Hardscratch,  about  7  miles  south  of  Point  Arena,  during  a  heavy  fog 
he  heard  a  steamer's  whistle  sounding  as  though  the  vessel  was  approaching  from 
the  southward.  It  was  about  11  p.  m.,  and  the  sound  led  him  to  believe  the  ves- 
sel was  close  in  shore  and  in  danger.  He,  with  his  party,  made  signals  with  a 
revolver  and  fog  horn  and  finally  heard  a  response  from  the  steamer,  she  being 
close  enough  for  the  order  "hard  a  starboard"  to  be  heard  plainly,  and  the 
response  of  "  all  right  ".  Those  on  the  vessel  had  not  heard  the  Point  Arena  fog 
signal,  which  was  in  operation,  the  sounds  being,  probably,  deflected  by  the  for- 
mation of  the  coast  line  in  that  vicinity. 

At  such  stations  as  Point  Boneta,  Point  Reyes  and  other  stations 
where  the  shore  line  is  bold  and  the  signals  are  placed  on  the  faces  of  steep 
bluffs,  on  or  off  which  the  prevailing  winds  blow,  the  inaudibility  of  the  fog 
signals  may  be  due  to  certain  facts  pointed  out  by  Mr.  W.  B.  Taylor  in  an  article 
on  "Recent  Researches  on  Sound,"  published  in  the  American  Journal  of  Science, 
3d  Series,  Vol.  XI. 

In  this  article  the  writer  gives  the  following  interesting  explanation  of  how  a 
sound  wave  will  be  deflected  by  the  retardation  of  a  current  of  air  by  friction: 


"  Figure  1  exhibits  the  more  ordinary  effects  of  a  favorable  wind  depressing  the  beam  of  sound  :  s 
being  the  signal  station  and  0  the  point  of  observation,  the  wind  blowing  from  E  to  IV,  As  the  spher- 
oidal wave-faces  become  more  pressed  forward  above  by  the  freer  wind  (assuming  it  to  be  retarded  at  the 
surface  by  friction),  and  as  the  direction  of  the  acoustic  beam  is  constantly  normal  to  the  successive  aerial 
surfaces  of  impact,  it  follows  that  very  minute  differences  of  concentricity  in  the  successive  waves  will  by 
constant  accumulation  gradually  bend  the  line  of  dynamic  effect  downward,  as  shown  in  the  sketch  on  a 
very  exaggerated  scale.  Of  the  sound  rays  represented  below  the  line,  some  will,  by  reflection,  reach 
the  observer's  ear  and  thus  increase  the  sound. 


33 


"  Figure  2  represents  the  ordinary  effect  of  an  opposing  wind,  here  blowing  from  IV  to  E.  The  wave 
faces  being  more  resisted  above  by  the  freer  contrary  wind  (assuming  as  before  a  surface  retardation),  the 
sound  waves  are  curved  upward,  and  the  lowest  ray  that  can  reach  the  distance  of  the  observer  at  o  is 
that  which  touching  the  surface  of  the  sea  is  gradually  so  lifted  upward  that  it  passes  above  the  ear  of 
the  listener,  leaving  him  practically  in  an  acoustic  shadow,  very  much  as  an  observer  on  the  deck  of  a 
vessel  when  losing  sight  of  the  hull  of  another  vessel  ten  miles  off  by  reason  of  the  interposed  convexity 
of  the  ocean,  stands  in  the  optical  shadow  of  the  earth.  In  both  cases,  if  the  conditions  favor,  the 
boundary  of  the  shadow  may  be  recrossed  by  ascending  from  the  deck  to  the  masthead,  and  the  sight  or 
the  sound  become  thus  regained. 


"Figure  3  represents  the  disturbing  effect  of  a  lower  contrary  wind  with  an  opposite  wind  above. 
In  this  case  the  principal  result  will  be  the  depression  of  the  sound  beam  as  in  figure  1,  but  more  strong- 
ly marked,  as  the  difference  of  motion  as  we  ascend  will  be  more  rapid.  Attending  this  action,  however, 
there  will  probably  be  some  lagging  of  the  lower  stratum  of  the  adverse  wind  by  reason  of  the  surface 
friction,  the  tendency  of  which  will  be  to  slightly  distort  the  lower  sound  radiations  by  giving  them  a 
reversed  or  serpentine  curvature.  The  upper  rays  of  sound  would  probably  have  only  a  single  declining 
curvature,  similar  to  that  shown  in  figure  1." 

On  this  coast  where  the  prevailing  winds  blow  on  shore  (z.  e. ,  from  the  south- 
west, west  and  northwest),  the  mariner  who  is  running  in  toward  the  land  would 
be  apt  to  find  the  circumstances  under  which  the  signal  was  audible  would  be 
similar  to  those  shown  in  Figure  1  of  the  preceding  diagrams.  That  is,  he  might 
hear  the  signal  at  dome  distance  from  the  shore  and  then  lose  it  as  he  approached 
nearer.  In  such  a  case  it  might  be  heard  again  from  the  masthead,  and  hence  it 
would  but  be  prudent  in  him  to  try  the  experiment.  -sofa  LibrsJCy 

The  varying  density  of  the  air,  due  to  the  increasing  or  diminishing  heat  of 
the  rising  or  setting  sun,  would  also  influence  the  direction  and  force  of  sound 
waves.  This  would  be  especially  noticeable  on  days  when  the  atmosphere  was 
partially  obscured  by  fog,  and  thus  rendered  what  Prof.  Tyndall  styles  "non- 
homcegeneous. "  Under  such  conditions,  as  Prof.  Henry  says  in  his  report  to  the 
Lighthouse  Board  in  1875,  "As  the  heat  of  the  sun  increases  during  the  first  part 
of  the  day,  the  temperature  of  the  land  rises  above  that  of  the  sea,  and  this  excess 


34 

of  the  temperature  produces  upward  currents  of  air,  disturbing  the  general  flow  of 
the  wind,  both  at  the  surface  of  the  sea  and  at  an  elevation  above." 

In  connection  with  the  subject  of  the  formation  of  fog,  the  study  of  the  tem- 
perature of  the  surface  of  the  North  Pacific  Ocean  off  the  coast  of  California  is  of 
interest,  and  from  a  paper  on  that  subject  by  Dr.  C.  M.  Richter,  read  before  the 
California  Academy  of  Sciences,  February,  1887,  and  published  in  the  following 
(June)  Bulletin,  No.  7,  of  the  Academy,  the  following  extracts  and  chart  are 
taken : 


TMmW'S^^S 


[  f  v&;  "      •  > ■  ■-  '  1    *--   :-^  ■■■•  -  ■       •  -    1    .-  >  -  ° 


"  The  question,  not  as  to  the  existence,  but  as  to  the  character  of  the  ocean 
currents  contiguous  to  the  coast  of  California,  is  still  an  open  one.  Some  of  the 
most  recently  published  maps  show  that  a  cold  current  of  great  width  washes  our 
shores,  and  others  again  indicate  that  it  is  the  deflected  warm  Japanese  current 


35 

which  is  passing  this  country  in  its  southward  movement.  A  third  opinion  gives 
the  surface  waters  to  the  Kuro  Siwo,  and  identifies  the  sub-stream  with  the  Polar 
current.        *       * 

' '  The  only  fact  which  emanates  from  these  observations  is,  that  a  surface 
current  of  a  southerly  direction  drives  the  waters  down  the  coast,  and  that  by 
strong  winds  from  the  south,  during  the  Winter  storms,  its  direction  may  be  tem- 
porarily reversed.       *       *       * 

' '  The  greatest  difference  in  the  temperature  of  the  surface  water,  between 
San  Diego  and  Trinidad  Head,  is  noticeable  nearest  the  shore.  The  following 
table  will  explain  it. 

Trinidad  Head.  San  Diego.  Difference. 

10  miles  off  shore 48. 50  59-8°  1 1-3° 

50     "      "       " 50.2  54.4  4.2 

100     "      "      "     54-o  59-9  5-9 

200     "      "      "      54.8  59.6  4.8 

1 '  The  temperature  increases  at  the  line  of  Trinidad  Head  gradually  from 
48. 50  10  miles  distant  from  shore,  to  54.80  220  miles  distant  from  shore,  indicating 
a  difference  of  6.30  between  the  two,  while  off  San  Diego  the  temperature  remains 
about  the  same. 

' '  The  ten  miles  off  shore  surface  temperature  of  Trinidad  Head  finds  its 
equivalent  ten  miles  off  San  Diego  at  a  depth  of  100  fathoms.  Following  the 
comparison — that  of  50  miles  off  Trinidad  Head  agrees  with  the  one  200  fathoms 
deep  50  miles  off  shore,  and  220  miles  off  shore  the  Trinidad  Head  temperature 
is  found  forty  fathoms  below  the  surface  on  the  San  Diego  line. 

"  Ten  miles  off  shore  the  ocean  has  an  avernge  depth  of  only  one  hundred 
fathoms,  with  the  exception  of  three  submarine  valleys — one  between  Trinidad 
Head  and  Point  Arena,  one  between  Point  Carmel  and  Point  Sal,  and  one  stretch- 
ing from  the  Santa  Barbara  channel  towards  San  Diego.  The  bottom  of  the  one 
hundred  fathom  plateau  has  an  average  temperature  of  450. 

"  Fifty  miles  off  shore  the  average  depth  of  the  ocean  is  1,000  fathoms.  At 
this  distance  the  existence  of  a  submarine  mountainous  grade,  which  is  highest 
in  latitude  of  Point  Carmel,  alters  the  isothermal  lines  of  the  ocean.  The  same 
action  on  the  temperature  of  the  water  is  repeated,  though  in  a  less  degree,  by 
another  submarine  grade  tending  southward  towards  San  Diego. 

The  result  is,  that  the  isothermal  line  of  400,  commencing  at  Trinidad 
Head  at  a  depth  of  about  350  fathoms,  and  which  is  found  to  be  off  San  Diego 
500  fathoms  deep,  sinks  off  San  Francisco  to  700  fathoms  depth,  and  off  Point 
Sur  still  deeper.  Therefore,  off  San  Francisco  and  off  Point  Sur  a  greater 
volume  of  warm  water  is  found  in  proportion  than  at  any  other  point  on  the 
coast.       *       *       * 

' '  The  analyzation  of  all  the  surface  temperatures  proves  the  existence  of  a 
cold  water  current,  about  150  miles  wide,  on  the  northern  boundary  line  of  Cali- 
fornia, passing  southward  nearest  the  coast  line,  which  is  reduced  in  width  con- 
stantly during  its  course,  until  it  reaches  Point  Conception,  where  it  is  partly 
deflected  to  the  southwest  and  partly  buried  by  warmer  surface  waters.  Its  tem- 
perature is  from  450  to  500  in  winter  time  nearest  the  coast,  before  Point  Arena  is 


36 

reached,  and  from  500  to  550  further  off  the  coast  and  until  it  is  submerged  north 
and  northwest  of  the  Santa  Barbara  channel. 

"To  the  west  and  south  of  this  cold  current  appears  a  great  body  of  warmer 
water,  having  a  temperature  of  from  55°  to  6o°  in  winter  time.  Its  direction 
seems  southerly  in  the  north  of  California,  and  is  doubtful  in  the  region  of  South- 
ern California.       *       *       * 

' '  This  investigation  reveals  *  *  "  the  reason  why  the  northern  part 
of  California  has  more  fog  in  summer,  and  probably  more  rain  in  winter;  it 
explains  the  reason  why  the  temperature  of  San  Francisco  cannot  sink  as  low  as 
that  of  Monterey;  it  reveals  the  causes  of  the  subtropical  climate  of  Southern  Cal- 
ifornia." 

*  *  *  "  The  practical  seaman  is  satisfied  by  the  knowledge  of  the  fact 
that  the  direction  of  the  waters  along  the  coast,  with  the  exception  of  those  near- 
est the  coast,  is  generally  southward,  and  northward  only  during  the  winter 
storms.  Adjacent  to  the  coast — at  a  distance  of  from  three  to  ten  miles  from  it — 
an  edd)r  current  is  observed  with  a  northerly  direction."  *  *  *  We  find 
on  the  chart  that  there  is  a  general  southerly  direction  of  the  surface  currents,  even 
next  to  the  coast,  north  of  San  Francisco.  The  under-surface  currents  show  no 
regularity  whatever  in  their  direction,  and  looking  at  this  chart  one  is  led  to 
believe  that  the  direction  of  the  arrows  is  given  for  the  purpose  of  proving  the  ex- 
istence of  a  whirlpool  in  the  ocean  near  the  coast  of  California." 

These  varying  currents  and  drifting  surfaces  of  unequally  heated  water  must 
have  a  very  important  effect  in  the  formation  or  dissipation  of  fog,  and  would  con- 
tribute to  the  formation  of  the  "wall  of  fog"  frequently  met  with  across  the 
entrance  to  San  Francisco  harbor,  and  other  points  on  this  coast. 


In  concluding  this  paper  on  the  subject  of  fogs  and  fog  signals  on 
this  coast,  the  writer  feels  that  he  cannot  render  mariners  a  better  service 
than  by  reprinting  the  remarks  made  by  Mr.  Johnson,  Clerk  to  the 
Light  House  Board  in  Washington,  in  the  paper  read  by  him  to  which  reference 
has  already  been  made.     Mr.  Johnson  says  : 

"While  the  mariner  may  usually  expect  to  hear  the  sound  of  the  average  fog 
signal  normally  as  to  force  and  place,  he  should  be  prepared  for  occasional  aber- 
rations in  audition.  It  is  impossible,  at  this  point  in  the  investigations  which  are 
still  in  progress,  to  say  when,  where,  or  how  the  phenomena  will  occur.  But  cer- 
tain suggestions  present  themselves  even  now  as  worthy  of  consideration . 

"It  seems  that  the  mariner  should,  iu  order  to  pick  up  the  sound  of  the  fog-sig- 
nal most  quickly  when  approaching  it  from  the  windward,  go  aloft;  and  that  when 
approaching  it  from  the  leeward,  the  nearer  he  can  get  to  the  surface  of  the  water 
the  sooner  will  he  hear  the  sound." 

It  also  appears  that  there  are  some  things  the  mariner  should  not  do. 

"  He  should  place  no  negative  dependence  on  the  fog-signal;  that  is,  he  should 
aiot  assume  that  he  is  out  of  hearing  distance  because  he  fails  to  hear  its  sound. 


37 

' '  He  should  not  assume  that  because  he  hears  a  fog-signal  faintly  he  is  at  a 
great  distance  from  it. 

' '  Neither  should  he  assume  that  he  is  near  to  it  because  he  hears  the  sound 
plainly. 

' '  He  should  not  assume  that  he  has  reached  a  given  point  on  his  course  be- 
cause he  hears  the  fog-  signal  at  the  same  intensity  that  he  did  when  formerly  at 
that  point. 

"Neither  should  lie  assume  that  he  has  not  reached  this  point  because  he  fails 
to  hear  the  fog-signal  as  loudly  as  before,  or  because  he  does  not  hear  it  at  all. 

"  He  shonld  not  assume  that  the  fog-signal  has  ceased  sounding  because  he 
fails  to  hear  it  even  when  within  easy  earshot. 

' '  He  should  not  assume  that  the  aberrations  of  audibility  which  pertain  to  any 
one  fog-signal  pertain  to  any  other  fog-signal. 

' '  He  should  not  expect  to  hear  a  fog-signal  as  well  when  the  upper  and  lower 
currents  of  air  run  in  different  directions;  that  is,  when  his  upper  sails  fill  and  his 
lower  sails  flap;  or  when  his  lower  sails  fill  and  his  upper  sails  flap. 

"  He  should  not  expect  to  hear  the  fog-signal  so  well  when  between  him  and 
it  is  a  swiftly  flowing  stream,  especially  when  the  tide  and  wind  run  in  opposite 
directions. 

"  He  should  not  expect  to  hear  it  well  during  a  time  of  electric  disturbance. 

' '  He  should  not  expect  to  hear  a  fog-signal  well  when  the  sound  must  reach 
him  over  land,  as  over  a  point  or  an  island. 

"And,  when  there  is  a  bluff  behind  the  fog-signal,  he  should  be  prepared  for 
irregular  intervals  in  audition,  such  as  might  be  produced  could  the  sound  ricochet 
from  the  trumpet,  as  a  ball  would  from  a  cannon;  that  is,  he  might  hear  it  at 
2,  4,  6,  8,  and  io  miles  from  the  signal-,  and  lose  it  at  i,  3,  5,  7,  9,  and  11  miles 
distance,  or  at  any  other  combination  of  distances,  regular  or  irregular. 

"These  deductions,  some  made,  as  previously  mentioned,  by  several  of  the  first 
physicists  of  the  age,  and  some  drawn  from  the  original  investigations  here  noted, 
are  submitted  for  consideration  rather  than  given  as  directions.  They  are  assumed 
as  good  working  hypotheses  for  use  in  further  investigation.  While  it  is  claimed 
that  they  are  correct  as  to  the  localities  in  which  they  were  made,  it  seems  proper 
to  say  that  they  have  not  been  disproved  by  the  practical  mariners  who  have  given 
them  some  personal  consideration,  and  who  have  tried  to  carry  them  into  general 
application.  Hence  these  .suggestions  have  been  set  down  in  the  hope  that  others 
with  greater  knowledge  and  larger  leisure  may  give  the  subject  fuller  attention, 
and  work  out  fuller  results. 

If  the  law  of  these  aberrations  in  audibility  can  be  evolved  and  some  method 
discovered  for  their  correction,  as  the  variations  of  the  compass  are  corrected,  then 
sound  may  be  depended  upon  as  a  more  definite  and  accurate  aid  to  navigation. 
Until  then,  the  mariner  will  do  well  when  he  does  not  get  the  expected  sound  of 
a  fog-signal,  to  assume  that  he  may  not  hear  a  warning  that  is  faithfully  given, 
and  then  to  heave  his  lead,  and  resort  to  the  other  means  used  by  the  careful  navi- 
gator to  make  sure  of  his  position." 


38 

The  following  article  in  relation  to  "  Collisions  in  Fogs,"  published  in  the 
Scientific  American  of  December  29th,  1888,  is  of  interest  to  all  ship-masters  and, 
being  germane  to  the  subject  treated  of  in  this  pamphlet,  is  quoted  in  full. 

"  In  his  annual  report  to  the  National  Board  of  Steam  Navigation,  President 
Cheney  shows  that  there  were  in  1887,  84  casualties  to  vessels  from  collisions  in 
fogs;  100  in  1886;  120  in  1885;  92  in  1884;  and  59  in  1883.  He  gives  a  statement 
by  Captain  H.  C.  Taylor,  U.  S.  Navy,  who  says: 

The  general  idea  on  shore  and  among  seafaring  people  who  do  not  reflect  and 
observe  closely  is  that,  if  you  are  going  slower,  you  can  stop  easier;  if  going  at  a 
high  rate  of  speed,  it  takes  longer;  but  the  real  fact  is  that,  for  all  purposes  of 
avoiding  collisions,  it  is  impossible  to  stop  at  all  when  at  high  speed,  within  any 
period  needed  to  avoid  collision. 

Those  who  have  practically  tried  it,  know  that  when  a  large  seagoing  vessel 
is  rushing  through  the  water  12  or  13  knot  speed,  that  the  first  effect  of  the  pro- 
pellor  or  paddle  wheels  backing  is  in  no  way  perceptible.  The  momentum  of  the 
ship  begins  to  be  lost  by  the  natural  resistance  of  the  water,  and  when  checked 
somewhat,  the  effect  of  the  screw  commences  to  be  felt,  and  not  before.  No 
heavy  vessels  (whose  momentum  becomes  so  great  as  their  speed  increases)  should 
go  more  than  six  knots  per  hour  in  a  thick  fog,  if  they  hope  to  avoid  collision; 
and  a  speed  of  eight  to  nine  knots  renders  avoidance  impossible. 

The  investigations  and  experiments  of  Captain  Colomb,  R.  N.,  with  many 
steam  screw  vessels,  of  different  size,  and  moving  at  different  speed,  show  that  the 
average  distance  in  which  a  steamer  will  stop  after  suddenly  reversing  the  engines 
is  four  and  one-half  times  the  ship's  length. 

Some  experiments  made  with  the  SS.  Aurania,  480  feet  long,  and  moving  at 
a  speed  of  thirteen  knots,  showed  that  she  came  to  a  dead  stop  in  three  and  six- 
tenths  times  her  length,  after  reversal  of  the  engines. 

The  case  of  the  Aurania  is  a  very  favorable  one,  and  indicates  that,  though 
not  at  full  speed,  she  stopped  in  one-third  (1,728  feet)  of  a  mile.  All  of  us  who 
are  familiar  with  thick  fogs  will  realize  the  uselessness  of  stopping  only  after  one- 
third  of  a  mile  has  been  covered. 

Experiments  with  the  SS.  Oregon  gave  the  same  results;  the  time  to  come  to 
a  dead  stop  being  3  minutes  and  59  seconds. 

The  mean  result  of  many  trials  with  different  sized  vessels,  and  moving  at 
different  speeds,  show  that  to  stop  a  vessel  in  the  shortest  possible  space,  the  helm 
should  be  put  hard  over  the  instant  the  engines  are  reversed.  If  this  is  done,  the 
vessel  will  lose  way  and  come  to  a  state  of  rest  when  she  has  changed  her  heading 
four  points.  She  will  then  have  moved  ahead  a  little  less  than  three  times  her 
length,  and  will  have  transferred  one  length;  that  is,  her  stern  will  be  just  clear  of 
her  original  course. 

The  dragging  action  of  the  rudder,  as  mentioned  above,  is  well  known  to  all 
seafaring  people,  and  can  generally  be  utilized  to  avoid  collision,  unless  danger 
exists  on  both  bows.  But  we  must  remember  that  the  above  results  were  obtained 
largely  in  quiet  weather  and  smooth  water;  and  a  strong  breeze  or  rough  sea  is 
liable  to  alter  the  above  results  as  to  the  movement  of  the  ship's  head." 


39 


The  substance  of  the  foregoing  paper  appeared  originally  in  the  Overland 
Monthly  magazine,  in  October,  1888.  In  extending  the  matter  to  form  this 
pamphlet  the  writer  wishes  to  acknowledge  his  obligations  to  Prof.  George 
Davidson,  Ass't  in  Charge  of  the  Pacific  Coast  Division  U.  S.  C.  &  G. 
Survey,  and  Captains  L,.  A.  Sengteller  andStehman  Forney,  Asst's  U.  S.  C.  &  G. 
Survey;  and  to  Commander  Nicol  Ludlow,  U.  S.  N.,  Inspector  of  the  Xllth  Light 
House  District  for  valuable  aid,  and  the  use  of  official  records  and  charts. 

The  San  Francisco  Pilots,  as  well  as  Captains  of  steamers  running  to  foreign 
and  Coast  ports  and  in  the  bay,  the  pilots  on  the  ferry  boats,  and  masters  of  ves- 
sels consulted,  have  given  much  valuable  information,  and  it  is  hoped  that  the 
present  attempt  to  present  the  result  of  their  experiences  will  be  of  service  to 
them  as  well  as  to  all  others  interested  in  the  commerce  of  the  Pacific  Coast. 

San  Francisco,  January,  1889. 


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